At least 55 of the around 70 people on board were killed in the accident, which happened in the early hours of Monday, local time.

Rescuers struggled to recover the bodies from the creek into which the bus had plunged.

Guatemalan President Bernardo Arévalo has declared three days of national mourning for the victims of the crash, one of the deadliest road traffic accidents in the region for years.

The bus normally covered the route between San Cristóbal Acasaguastlán and Guatemala City, officials said.

On Monday it had reportedly left the village of San Antonio La Paz at around 04:00 local time.

About 30 minutes later, on the outskirts of Guatemala City, it plunged 20m (65ft) from a bridge into a creek carrying wastewater.

Photos from the scene show the bus, lying on its roof, wheels in the air, in the shallow water.

Local media said the bus had been full of students, commuters, and people on their way to the capital for medical appointments.

As news of the accident spread, worried relatives gathered at the foot of the bridge waiting for news of their loved ones.

One woman told Guatemalan news site La Hora that her 67-year-old husband had set off at four in the morning but had never made it to work.

Another woman had identified the body of her brother, who had been on board the bus.

Rescue workers said they had retrieved 53 bodies so far.

Two people who had been rescued alive from the wreck died in hospital, bringing the total number of dead to 55.

The 24-year-old driver is reportedly among those who died.

Eyewitnesses described seeing the vehicle crash into two cars before it hit the guardrail and fell into the precipice.

Investigators said they would check if the driver could have lost control due to a brake failure.

Guatemala’s communications minister, Miguel Díaz Bobadilla, told reporters the bus was around 30 years old but had a valid licence for carrying passengers.

Díaz Bobadilla added that officials were checking if it may have carried more weight than it should have.

Police are also investigating a gun they found on board the bus.

The discovery of the weapon has given rise to speculation in local media that the driver may have panicked or been injured when he was threatened with the gun.

The deputy director-general of Guatemala’s National Civil Police, Helver Beltetón, said the gun was registered to one of the deceased passengers, who worked as a private security guard.

Beltetón said that police were not “ruling out any hypothesis”.

He added that “the brakes could have failed but we’re also not ruling out an accident or a criminal act, all that will be investigated”.