Riot police clashed with rock-throwing demonstrators in central Athens on Thursday, sending Christmas shoppers and people in cafes running for cover. Frightened parents scooped up their children from a Christmas carousel in the city's main square and fled.

The protesters broke away from a peaceful rally and hurled rocks and firebombs at police and buildings near parliament, overturned a car and set fire to trash bins. They also splashed police with red paint.

Police responded with tear gas.

Firefighters and police also rushed to stop protesters from burning down the city's main Christmas tree, which was just replaced earlier this week after the first was torched in riots. Families abandoned the carousel in downtown Syntagma Square after happily going on rides all morning.

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Thursday's clashes were the latest outbreak of violence after the police's fatal shooting Dec. 6 of 15-year-old Alexandros Grigoropoulos. Protests over the boy's death and the increasing economic hardship in Greece have led to the worst rioting the country has seen in decades.

Hundreds of businesses have been smashed, burned or looted and gangs of youths fought running battles with riot police firing tear gas every night for a week.

The riots have been fed by dissatisfaction with Greece's increasingly unpopular conservative government. Protests groups have issued a range of demands, from disarming police to greater income support for low-earning families.

Before the violence broke out, some 7,000 students and other protesters marched in a rally Thursday, chanting "We are the law, we'll stay on the streets." As they passed, fearful shop owners shuttered their store fronts. Some demonstrators painted white crime-scene-style body outlines on the streets.

Earlier in the day, some 1,000 demonstrators joined a Communist Party-backed peaceful march through Athens. Some 300 people were also marching in heavy rain in Greece's second largest city of Thessaloniki in the north.

Major labor union staged work stoppages Thursday to protest the shooting and the conservative government's economic policies.

As part of the strikes, air traffic controllers walked off the job for three hours, forcing state Olympic Airlines to cancel 28 flights and reschedule another 14. State hospitals were operating with skeleton staff due to a 24-hour strike.

The government appealed for calm after another teenager was shot in the hand late Wednesday near his school. It was unclear who shot him.

Police spokesman Panayiotis Stathis said no officers had been in the area at the time of the attack and Interior Minister Prokopis Pavlopoulos promised a quick and thorough investigation. The boy underwent surgery Thursday.