Downtown Belgrade reverberated with the piercing sound of whistles and vuvuzelas on Saturday as huge crowds converged for a major anti-government rally targeting populist President Aleksandar Vucic. The demonstration, seen as the climax of months of near-daily protests against corruption, marks the most significant challenge to Vucic’s 13-year authoritarian rule.

Tensions escalated when police arrested a man who drove his car into a crowd of protesters in a Belgrade suburb, injuring three. Ahead of the rally, Vucic warned of alleged plans for unrest, threatening arrests and severe penalties. In an apparent bid to deter attendance, Belgrade’s public transport was halted “for security reasons,” while roads into the city were clogged with traffic.

The protests, sparked by a deadly train station canopy collapse in northern Serbia on November 1 that killed 15, have been led by students decrying government corruption and negligence. On Friday, tens of thousands cheered students who marched or cycled from across Serbia to join Saturday’s rally. From early morning, people gathered across the city, preparing to march downtown.

Fears of violence loom as Vucic’s supporters, including ex-paramilitary members tied to the 2003 assassination of Serbia’s first democratic premier and notorious soccer hooligans, camped near his headquarters. Footage from N1 television showed young men with baseball bats entering the pro-Vucic site. Interior Minister Ivica Dacic reported 13 overnight detentions, including six opposition activists accused of plotting a coup.

Vucic has blamed Western intelligence for the unrest, a claim resonating little with citizens disillusioned by corruption and failing institutions. The student-led movement has galvanized widespread support, with prior rallies in other cities drawing peaceful, massive crowds. As Belgrade braces for the showdown, Serbia stands at a critical juncture.