Opponents of Serb President Aleksandar Vucic broke into the state-run RTS television building on Saturday, demanding to address the population, in images aired live.
There have been weekly opposition protests since December against what they describe as Vucic's slide towards autocratic rule, while accusing RTS of pandering to the ruling party and demanding more airtime for opposing views.
Among the dozens who invaded RTS on Saturday were opposition figures including former Belgrade mayor Dragan Djilas and Bosko Obradovic, leader of the right-wing Dveri party.
Interior Minister Nebojsa Stefanovic denounced the action in a statement run on RTS.
Private TV channel N1 showed images of police starting to remove the protestors from the RTS premises.
Earlier thousands marched peacefully through the centre of Belgrade as they have done on each Saturday since December 8.
Protests were also held in several other Serbian towns, with the marchers accusing those in power of muzzling the media and civil rights groups, also calling for the RTS chiefs to step down.
Vucic, an ultra-nationalist-turned-pro-European, has rejected claims he has become autocratic, and in return has launched a "Future of Serbia" campaign, visiting towns throughout Serbia and championing his policies.
The European Commission last year raised concerns about media freedoms in Serbia, denouncing threats, intimidation and violence against journalists.