The shells of burnt out cars littered the front of Hungary's state TV headquarters in Budapest on Tuesday, following protests overnight.
Police sniffer dogs checked the vehicles for traces of explosives before the clean-up began.
The demonstrators had gathered on Monday for an initially peaceful demonstration to demand the resignation of Prime Minister Ferenc Gyurcsany.
Trouble began at the television station, when a small group of protesters tried to hand in a petition.
A clash with riot police ensued and the square rapidly filled with mainly young people.
A small crowd threw stones and bottles and broke the building's windows.
The battles were fierce. More than 100 police were among the 150 people reported injured.
The protesters were able to gain access to the building, which they ransacked before police regained control.
Several cars outside the building were torched.
Police used water cannon and teargas against the protesters, who were angry at Mr Gyurcsany's admission that his Socialist government told lies to win an election.
These are the first such clashes to take place in Hungary since the fall of communism and the establishment of democracy in the late 1980s.