Masked youths hurled firebombs and chunks of marble at police during a protest in Athens to mark the first anniversary of the police shooting of a teenager whose death caused widespread riots.

Police fired volleys of teargas to disperse the youths in running street battles in the centre of the capital as several thousand demonstrators marched to commemorate the death of 15-year-old Alexandros Grigoropoulos. The teenager's death sent youths rampaging through cities for two weeks last December.

, the rioters smashed bank windows, and overturned rubbish bins and set them alight as they hurled rocks and firecrackers at riot police.

Authorities said 134 people were detained for public order offences in Athens and 80 in the northern city of Thessaloniki, where a similar demonstration also ended in violence, with youths throwing petrol bombs at police and setting fire to cars.

At least five protesters were injured in the clashes, including a woman who was hit by a police motorcycle. Police said 16 officers were hurt. More than 6,000 police officers had been deployed across Athens in an effort to prevent violence.

Police on motorbikes chased rioters amid scenes of chaos at Syntagma square in Athens, with youths punching and kicking officers pushed off their bikes.

One policeman who lost control of his motorbike struck a female pedestrian, who was injured and taken to hospital.

At Athens University, masked protesters broke into the building and pulled down a Greek flag, replacing it with a black-and-red anarchist banner.

The dean of Athens University was injured when the youths broke into the building, and was in intensive care in hospital, authorities said.

As night fell, about 200 masked demonstrators were holed up in the neoclassical university building, smashing marble chunks off the university steps and ripping up paving stones from the courtyard to use as missiles against the police.

A football match at Athens Olympic stadium between local clubs Panathinaikos and Atromitos was suspended for 30 minutes because of teargas used by police against rioters outside the ground.