Thousands of people have been fleeing “multiple active conflict zones”, the UN refugee agency, UNHCR, said.

The aid agencies said their warehouses with food and medical supplies have been looted as M23 rebels continue to battle to take control of the city.

Anger has been growing over the M23 offensive, and calls for peace talks to end the fighting are mounting.

“Hospitals are overwhelmed. There are currently hundreds of people in hospital, most admitted with gunshot wounds,” the Reuters news agency quoted Adelheid Marschang, the World Health Organization’s emergency response coordinator for the Democratic Republic of Congo, as saying.

The International Committee of the Red Cross (ICRC) said its hospital received more than 100 wounded in just 24 hours, a number it previously received over the course of a month.

It said this had forced its staff to turn the hospital car park into a triage unit.

The use of heavy artillery in densely populated areas is causing severe injuries, particularly among children, it added.

• What’s the fighting in DR Congo all about?

Both the ICRC and the World Food Programme say their warehouses have been looted in recent days.

Reports say at least 17 people have been killed and close to 400 wounded.

On Tuesday, South Africa said that four more of its soldiers, who are in DR Congo as part of peacekeeping efforts, had died as a result of clashes with the M23.

This brings the total number of South African casualties to 13. Malawi and Uruguay have also lost peacekeepers.

South Africa’s President Cyril Ramaphosa on Monday spoke to his Rwandan counterpart Paul Kagame, with the two agreeing on an urgent need for ceasefire and resumption of peace taks

The African Union is also set to host an emergency meeting later on Tuesday.

Late on Monday, DR Congo President Félix Tshisekedi held a meeting with leaders of some state institutions to evaluate the situation in the city.

“Our soldiers and the [pro-government militia] Wazalendo continue to hold certain positions in the city” said Vital Kamerhe, the speaker of the National Assembly after the meeting.

He said the president would address the nation later on the matter, without giving specific details.

Since Friday, Goma has been cut off from electricity and water, and Mr Kamerhe said the government was working hard to restore them to the city.

He said the government was also seeking diplomatic and political solutions to the crisis.

It came as the new US Secretary of State Marco Rubio condemned the M23 attack in a call with Tshisekedi.

In a statement, the US State Department said the Congolese leader agreed on the need to restart peace talks “as soon as possible” with Rwanda, which is accused of backing the rebels.

Mr Rubio also spoke to Kenya’s President William Ruto, agreeing to push forward peace talks. A meeting called by the Kenyan leader between Tshisekedi and Kagame has been scheduled for Wednesday.

The Congolese government has also asked for another meeting of the UN Security Council – demanding that this time it take tough action against Rwanda

During an emergency UN meeting on Sunday, DR Congo demanded sanctions against Rwanda, saying its forces had crossed into its territory in what amounted to a “declaration of war”.

Following the meeting, the UN condemned M23 advances and the “ongoing flagrant disregard for the sovereignty and territorial integrity of the DR Congo”, including the presence of “external forces”.

Rwanda has in the past denied direct support for the M23, but the UN peacekeeping chief Jean-Pierre Lacroix has said there is no doubt its troops were supporting the rebels.

In the capital Kinshasa, angry protesters on Tuesday burned parts of the French embassy, to express discontent over the M23’s offensive.

They stormed the streets, restricting circulation, and burning tyres and disrupting traffic.

Plumes of smoke could be seen billowing as parts of the embassy went up in flames.

Some residents preferred to observe a day of the “dead city”, following a call by civil societies to stay at home in solidarity with Goma.

The fate of the economic and trading hub Goma is still unclear. UN officials have said the situation is chaotic with fighting continuing in parts of the city.

A Congolese government official has said the army is still in control of most of the regional capital, but M23 rebels who have attacked the city dispute that.

Reports say at least 17 people have been killed and close to 400 wounded.

On Tuesday, South Africa said that four more of its soldiers, who are in DR Congo as part of peacekeeping efforts, had died as a result of clashes with the M23.

This brings the total number of South African casualties to 13. Malawi and Uruguay have also lost peacekeepers.

South Africa’s President Cyril Ramaphosa on Monday spoke to his Rwandan counterpart Paul Kagame, with the two agreeing on an urgent need for ceasefire and resumption of peace taks

The African Union is also set to host an emergency meeting later on Tuesday.

Late on Monday, DR Congo President Félix Tshisekedi held a meeting with leaders of some state institutions to evaluate the situation in the city.

“Our soldiers and the [pro-government militia] Wazalendo continue to hold certain positions in the city” said Vital Kamerhe, the speaker of the National Assembly after the meeting.

He said the president would address the nation later on the matter, without giving specific details.

Since Friday, Goma has been cut off from electricity and water, and Mr Kamerhe said the government was working hard to restore them to the city.

He said the government was also seeking diplomatic and political solutions to the crisis.

It came as the new US Secretary of State Marco Rubio condemned the M23 attack in a call with Tshisekedi.

In a statement, the US State Department said the Congolese leader agreed on the need to restart peace talks “as soon as possible” with Rwanda, which is accused of backing the rebels.

Mr Rubio also spoke to Kenya’s President William Ruto, agreeing to push forward peace talks. A meeting called by the Kenyan leader between Tshisekedi and Kagame has been scheduled for Wednesday.

The Congolese government has also asked for another meeting of the UN Security Council – demanding that this time it take tough action against Rwanda

During an emergency UN meeting on Sunday, DR Congo demanded sanctions against Rwanda, saying its forces had crossed into its territory in what amounted to a “declaration of war”.

Following the meeting, the UN condemned M23 advances and the “ongoing flagrant disregard for the sovereignty and territorial integrity of the DR Congo”, including the presence of “external forces”.

Rwanda has in the past denied direct support for the M23, but the UN peacekeeping chief Jean-Pierre Lacroix has said there is no doubt its troops were supporting the rebels.

Forty-year-old Denise Kabeya lives in the Panzi area in DRC’s western Kwango province – where health authorities say most cases of the unknown disease have emerged since October.

That month, Kabeya’s 12-year-old daughter Diane fell ill.“My beloved little one had headaches, runny nose, no appetite and was physically weak,” Kabeya said. “I thought it was malaria and typhoid fever,” she shared, explaining that those diseases are endemic in the region.

When Diane developed a blocked nose, Kabeya hoped the worst was over and that she would make a speedy recovery, as was usually the case when she developed such symptoms. But the child complained about more aches and pains, and eventually passed away from her illness in late October.

Between October 24 and December 11, there were 514 cases of the undiagnosed disease reported in eight of the 30 health areas in Panzi health zone, according to figures from the local health authorities.

Earlier this week, the WHO, which has sent experts to the region to investigate the cause of the outbreak and help with the response, said more than 30 people had died in hospitals from the disease.

There were another 44 deaths recorded in remote communities in Panzi, Congolese Minister of Health Roger Kamba said last week.Kamba said the outbreak was first reported in October, with the alert level raised to high at the end of November.

Most of the cases and deaths are in children under 14, national health authorities said, with children under five presenting with the majority of cases.

Because so little is known about this mystery disease, it is difficult to know why children are so vulnerable, experts said.

Speaking at a media conference last week, Kamba said that the disease is flu-like.

“Respiratory distress was noted in some children and some other people who died,” Kamba, said, noting that some patients were anaemic, which was the cause of some of the deaths linked to the disease.

 Cases of severe malnutrition have aggravated the disease in some children, according to local sources in Panzi, information also corroborated by the national Ministry of Health.

“Symptoms are flu-like. Patients suffer from high fever, headaches, coughing, runny nose and aches and pains,” Serges Zenga, an attending physician in the Kenge health zone, near Panzi, told Al Jazeera.

This week, WHO Director-General Tedros Adhanom Ghebreyesus said laboratory samples from infected people were being collected and tested. So far, most of the samples had tested positive for malaria, he said, but added that it was possible more than one disease was involved.

Meanwhile, the remoteness of the epicentre of the outbreak, as well as a lack of infrastructure, was jeopardising the fight against the disease.

Teams of laboratory technicians, epidemiologists from the Health Ministry and some of the Congolese government’s partners, including the WHO, are already deployed in the field, with a view to identifying the disease and reinforcing efforts to combat it.But located some 700km (435 miles) away from DRC’s capital, Kinshasa, the Panzi health zone is “rural and remote” and difficult to access, the WHO said – a feat made tougher by poor road conditions.

“We sent a team into the field. The team took two days to reach the area because the road is very bad in the rainy season,” Kamba said.

Additionally, rural Panzi lacks testing capacity, meaning that samples have to be taken to laboratories in Kikwit, more than 500km (310 miles) away.

The WHO said limited diagnostics in the region have delayed the identification of the underlying cause of the outbreak. However it added that its teams were helping with patient treatment, risk communication and engagement with the community as the health crisis continued.

Meanwhile, on the ground, medics say there are huge difficulties in caring for patients who are bedridden at Panzi hospital.

“We don’t have resuscitation kits such as oxygen condensers, we don’t have treatment centres and isolation facilities, and we don’t even have electricity; [there is] scarcity of communication tools and internet,” Dr Rufin Mukuwa, a doctor at the Panzi general referral hospital, told Al Jazeera.

Speaking to Al Jazeera by phone from Kenge, the capital of Kwango province, some residents said they feared the outbreak spreading from remote Panzi into their communities.

“We’re worried that the provincial authorities haven’t taken preventive measures to prevent this disease from spreading to other areas,” resident Emile Yimbu complained.

He called for the reinforcement of epidemiological surveillance measures to contain the disease within a well-defined zone, and lessen its consequences.

Prosper Kiswemba, a local councillor in Kenge, is also worried about how end-of-year travel plans in the region may affect the potential spread of the disease.

Kiswemba said hygienic measures such as temperature sampling and the installation of hand-washing stations along arterial roads leading to Panzi needed to be reinforced, lest the disease spread further.

Meanwhile, one local health expert who spoke to Al Jazeera on condition of anonymity, said they feared the disease may be zoonotic in origin.

Even though national and global health bodies have not announced any animal-related links, the expert said: “Most of the people I’ve interviewed personally admit to having been in contact with certain wild animals a few days before falling ill.”

To be safe, he said people should be cautioned about reducing contact with wild animals.

As the mystery disease spreads, patients in Panzi health zone are also suffering from a number of other diseases, including typhoid fever and measles, doctors said.

The timing of this new outbreak has some local health facilities overwhelmed, a local medical source told Al Jazeera.

Mukuwa at Panzi general hospital, however, sees the outbreak as a worrying but surmountable challenge.

“We are receiving numerous cases, varying between 15 and 20 patients a day,” he said.

He sees some symptoms of the disease – like respiratory issues – as being similar to those of COVID-19, and said patients at the hospital are being treated according to the signs and symptoms they present with.

“For example, we use azithromycin, amoxicillin or spiramycin for respiratory complications. If patients come in with headaches, we use paracetamol to relieve them,” he explained.

This has brought some relief, he said, while investigations into the outbreak continue.

Two years ago, Panzi suffered an epidemic of typhoid fever. The area also has high levels of malnutrition and low vaccination coverage, meaning children are vulnerable to a range of diseases, the WHO’s Tedros said this week.

This new disease comes as doctors in the DRC are still tackling the ongoing mpox epidemic, with at least 40,000 cases recorded and more than 1,000 deaths reported.