Several thousand people have marched through the Greek capital Athens to protest at the government's economic policies, as part of a general strike.
While turnout appeared lower than expected, the strike hit transport and the public sector and the city saw new unrest over the shooting of a teenager.
Rioters hurled petrol bombs at police outside a court where two policemen were remanded in custody for his death.
A defence lawyer says the youth was killed by a ricochet.
Police officer Epaminondas Korkoneas, 37, has been charged with murder
Greece's conservative prime minister has vowed to restore order and compensate businesses affected by the riots, which spread from Athens across Greek cities after the shooting on Saturday.
The leader of the socialist opposition, George Papandreou, made a call for public calm.
A lawyer for the officer who fired the shot which killed 15-year-old Alexandros Grigoropoulos, who was buried on Tuesday, said ballistics tests on the fatal bullet had shown the death was an accident.
Police officer Epaminondas Korkoneas, 37, was charged with murder and police officer Vassilios Saraliotis, 31, was charged as an accomplice. The Athens court ordered both men to be held in jail pending their trial. No date for the trial was set.
The ballistics tests have not yet been published and the Grigoropoulos family has hired an independent pathologist to study the case to ensure there is no cover-up.
The two main umbrella unions - the Greek General Confederation of Workers (GSEE) and the Civil Servants Supreme Administrative Council (ADEDY) - are demanding increased social spending in light of the global financial crisis, as well as higher wages and pensions.
Athens international airport closed
Athens bus, metro and suburban train systems disrupted
Teachers, journalists, bank clerks and public sector workers also expected to strike
The bombs were reportedly thrown as a defence lawyer was preparing to talk to reporters outside the building.
An Associated Press reporter witnessed running battles in the city centre as masked youths pelted police with rocks, bottles and blocks of marble smashed from a metro station entrance.
Windows newly replaced after four nights of rioting were smashed again.
"The government wanted us to postpone this protest, but they are the ones who have to do something to stop this violence and to improve the quality of our lives," said one demonstrator, drama student Kalypso Synenoglou.
High-school students chanting "Cops! Pigs! Murderers!" clapped and cheered each time a riot policeman was hit by a stone, AP adds.
Also on Wednesday, a group of about 100 Roma attacked a police station in the impoverished Athens suburb of Zefyri, where they attempted unsuccessfully to push a burning lorry into the station, Greek TV reports.
And in the port city of Patras, 215km (134 miles) west of Athens, a crowd of shop-owners is said to have turned on rioters and forced them to stop a wave of destruction, our correspondent says.
Entrepreneurs have been sleeping in their shops to defend them against rioters and looters.
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