Protesters stormed the headquarters of public television MTV on Szabadság tér during the night, forcing it off the air, as they demanded the resignation of Prime Minister Ferenc Gyurcsány.
The demonstrators reportedly wanted to hand MTV's news director a petition to be read live on air.
The crowd of about 10,000 eventually set fire to several cars and beat back police who tried to clear the square in front of the building.
Police cleared the building by 3:30 a.m. and is now guarding the area against further incidents.
Over 125 people, including about 100 police officers, have been hospitalized after clashes between demonstrators and police, a spokesman for the National Ambulance Service said. Most injuries were bruises caused by rocks or lacerations caused by glass.