Fifteen people were killed were killed on November 1 when a roof collapsed at a train station in the city of Novi Sad, fuelling longstanding anger over corruption and nepotism.

Since  then, mass demonstrations have grown into Serbia’s largest protest movement in years and represent a threat to populist President Aleksandar Vucic’s decade-long grip on power.

In the near-freezing temperatures, students arrived in Kragujevac from across Serbia by bus and even on foot, beating drums, blowing whistles, and holding up the country’s flag.

The protesters planned to block one of the city’s main boulevards for 15 hours and 15 minutes, in a tribute to the train station victims. They also held 15 minutes of silence.

“We are here to fight for a better tomorrow, against corruption,” said 20-year-old Jovan, who drove from the capital Belgrade.

Student protestors have enjoyed broad support from Serbia’s public, many of whom blame the Novi Sad tragedy on corruption and nepotism within Vucic’s government, allegations authorities deny.

Verica, a 52-year-old professor from the city, joined the protest with her teenage daughter.

“I have not been so happy and proud for a long time,” she said. “I am proud of their persistence.”

The university student-led movement has put increasing pressure on Serbia’s government, spurring the resignation of several high-ranking officials, including Prime Minister Milos Vucevic at the end of January.

Elsewhere, 13 people have been charged over the train station disaster. But this has done little to quell the demonstrations.

Since the accident, students have staged daily protests, taking over university buildings and blocking highways and squares.

“We  will stay here until the blockade ends,” said Djordje Vujovic, 22, a mechanical engineering student.

The students are demanding that authorities publish documents relating to the station roof collapse. They also want justice for those responsible, the dismissal of charges against protesting students, and a greater budget for higher education.

Ivan and Ivana, 23-year-old mathematics students, were among a group of about 400 people who had walked for four days to reach Kragujevac from Belgrade.

“We wanted to show the people living in the country that we support them,” Ivan said. “We do not think only about the people in Belgrade.”