At least 100,000 people have converged in Belgrade for a massive rally in the Serbian capital seen as a culmination of months-long protests against populist President Aleksandar Vucic.

The Serbian president conceded the need for "change" after the largest demonstrations in decades hit Belgrade.

Hundreds of thousands of people descended on Serbia's capital on Saturday to protest over the deaths of 15 people in a railway station collapse. While the government put attendance at 107,000 across Belgrade, an independent monitor said 325,000 - if not more - had gathered, making it Serbia's largest protest ever.