Tens of thousands of people streamed into a central square in Serbia's capital on Sunday for a rally against populist President Aleksandar Vucic and his government, whose tight grip on power has been challenged by weeks of street protests led by university students.

The rally at Belgrade's Slavija Square, one of the largest in recent years, was called by students and farmer unions. It was part of a wider movement demanding accountability over the November 1 collapse of a canopy at a railway station in the country's north that killed 15 people.

“We are all under the canopy,” read one of the banners displayed at the main Belgrade square.

Smaller rallies were also held in the cities of Nis and Kragujevac. The protest in Belgrade started with a 15-minute silence for the victims. Later, chants of “You have blood on your hands!” were heard.

Many in Serbia blame the collapse on widespread corruption and sloppy work on the railway station building in the city of Novi Sad.

In a show of confidence, the Serbian president on Sunday inaugurated a section of a newly-built highway in central Serbia.

Vucic said he wouldn't budge to opposition demands for a transitional government and accused his opponents of using students to try to seize power.

“We will beat them again,” said Vucic. “They (the opposition) don't know what to do but to use someone's children.”

In an apparent attempt to defuse the student-led protests, Vucic has been advertising what he said are “favourable” loans for young people to purchase apartments as well as attracting tens of thousands of doctors and other skilled people who have left the Balkan country for a better life in the West in recent years.

Prosecutors have arrested 13 people over the Novi Sad tragedy, including a government minister whose release later fueled public scepticism about the honesty of the investigation. (AP)