Thousands stood in silence for fifteen minutes in the southern city of Nis in Serbia to commemorate those killed in a railway station disaster in November, in a student-led protest that has grown into the biggest threat yet to the country’s president’s grip on power.

Mass demonstrations have gathered momentum in the country since 15 people were killed when a roof collapsed at a newly renovated train station in Serbia’s second-biggest city, Novi Sad.

On Saturday, hundreds of students marched, ran, or rode bikes to Nis, visiting various towns on their way and gaining the support of people living outside the country’s urban centers.

From the early hours of Saturday morning, residents had also set up improvised stalls across the city’s streets, offering food and refreshments to the crowds streaming through, waving flags, carrying banners against corruption, and blowing whistles and vuvuzelas.

At 11:52 local time (10:52 GMT), the time when the tragedy occurred, everyone gathered in the city’s central square to pay tribute to the victims by standing silent for 15 minutes.

After that, music echoed through the city as loudspeakers blared chants of “Serbia has risen” and “Pump it,” a slogan symbolizing the students’ resolve to keep protesting.

“This is the way to make a revolution,” Tarek, a 22-year-old graphics designer from Novi Pazar, told the Reuters news agency.

“It is the right way to achieve the change, to create a better future, a functional state without corruption.”

Many Serbians have blamed the tragedy on corruption they link to President Aleksandar Vucic’s decade in power. Teachers, farmers, and other workers have joined the protests that began with a student blockade of classes at state universities in December.

Prime Minister Milos Vucevic and two other ministers have also resigned over the protests that have taken place in the capital, Belgrade, as well as in towns across the country.

So far, prosecutors have charged 13 people in connection with the roof collapse.

“I hope for justice,” Emilija Jovanovic, a 21-year-old student, told the AFP news agency.

“We expect change,” Aleksandar Arandjelovic, a 34-year-old lawyer from Nis, added.

President Vucic and other government officials have switched between issuing calls for talks and also firing off allegations that the demonstrators are being backed by foreign powers.

“A lot of money has been invested in the color revolution,” Vucic said on Friday while speaking to his supporters in Knjazevac, some 50 km (31 miles) away from Nis.

To quell the protests, the government has sought to meet several of the student organizers’ demands.

Those steps have included releasing a number of documents related to the renovations at the station; pardoning protesters arrested at rallies; boosting funding for higher education; and launching criminal proceedings against suspects accused of attacking demonstrators.

But students, who have emerged as the leaders of the protests, aim to continue their daily demonstrations. They also want charges against the protesting students to be dismissed and an increased budget for higher education.