Serbian police have fired tear gas at anti-government protesters in downtown Belgrade as they clashed for the third day on the streets of the country's capital and other cities amid reports of police brutality and excessive use of force during the unrest.

Anti-corruption protesters in Serbia set fire to the Valjevo offices of the country's ruling political party, city leaders said, amid clashes sparked by the deadly collapse of a rail station in November.

Serbia's police used teargas and crowd control vehicles on Friday evening in Belgrade to disperse anti-government protesters who threw firecrackers and flares at police officers in what is seen as a major escalation of the nine-month-long protests.