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ATHENS, Greece - Gangs of youths smashed their way through central Athens and Thessaloniki on Monday, torching stores and buildings after the fatal police shooting of a teenager sparked Greece's worst rioting in decades.

Dozens of shops, banks and even luxury hotels had their windows smashed and burned in a night of lawlessness as youths fought running battles with riot police. Black smoke rose above the city center, mingling with clouds of tear gas.

Prime Minister Costas Karamanlis, whose increasingly unpopular government has already faced a growing number of sometimes violent demonstrations in recent months, called an emergency Cabinet meeting Monday night.

In Athens, rioters torched the capital's massive Christmas tree in central Syntagma Square. As the hooded youths moved on, some protesters posed for photos in front of the blaze, and others sang the Greek version of "O Christmas Tree."

The windows of two of Athens' luxury hotels, the Athens Plaza and the Grande Bretagne on Syntagma Square, were smashed. A hotel guard at the Athens Plaza said its guests had been evacuated.

A lone man with a bucket of water struggled to extinguish a fire in the ground floor of the Foreign Ministry, opposite Parliament. Fires were also reported in the building of an airline and a Greek bank, as well as in tens of other stores in most of Athens' major central streets.

Rioters, meanwhile, set up burning barricades across downtown streets.

Scenes of destruction also unfolded in Thessaloniki, where hundreds of masked and hooded youths hurled rocks and molotov cocktails at storefronts and riot police, who responded with tear gas.

The fire departments of both cities rushed to respond to the widespread destruction. In Athens, rioters surrounded one small fire truck as it tried to extinguish a blaze, smashing the truck's windows before setting it alight.

Elsewhere, rioters looted a store selling hunting weapons and swords.

Greek media also reported fires and destruction in the central city of Larissa.

Massive riots first erupted Saturday across the country, from Thessaloniki in the north to the island of Crete in the south, after 15-year-old Alexandros Grigoropoulos was fatally shot by a police officer in Athens' often volatile Exarchia district.

The circumstances surrounding the shooting are unclear, but the two officers involved have been arrested; one has been charged with murder and the other as an accomplice. A coroner's report shows the boy was shot in the chest.

Schools were to shut Tuesday in mourning, while staff at universities declared a three-day strike.

The Police Officers' Association has apologized to the boy's family, and President Karolos Papoulias sent a telegram to his parents expressing his condolences.

"All the dangerous and unacceptable events that occurred because of the emotions that followed the tragic incident cannot and will not be tolerated," Karamanlis said in a live televised address Monday morning. "The state will protect society."

But his calls for calm went unheeded and the scenes of destruction are likely to further dent the government's popularity.

In an outpouring of rage, high school and university students join self-styled anarchists in throwing everything from fruit and coins to rocks and Molotov cocktails at police and attacked police stations throughout the day.

"Cops! Pigs! Murderers!" protesters screamed at riot police.

Abroad, demonstrators raised banners at the Greek Embassy in London and the black-and-red anarchist flag at the Greek consulate in Berlin.

Separately, about 10,000 protesters from the Communist Party of Greece and another left-wing party marched through the center of Athens.

With the global financial crisis hitting Greek consumers, shop owners worried the violence would hurt consumer confidence.

"It comes at a time when we have been trying so hard to establish a Christmas spirit in the market," said Vassilis Krokidis, head of the Piraeus Traders' Association. "Our challenge remains getting through the economic crisis and saving the jobs of those who work in regular businesses."

One assistant at a china shop watched in fear as rioters attacked her store.

"Nobody seems to care about the employees at the burnt shops, what will their fate be now over the Christmas season?" said the woman, who gave her name only as Eleni.

Although there is little public support for street violence or wanton destruction of property, there is a deep well of tolerance for demonstrations in Greece, where the right to protest is held dear.

Violence often breaks out between riot police and anarchists during demonstrations. Anarchist groups are also blamed for late-night firebombings of targets such as banks and diplomatic vehicles. The attacks rarely cause injuries.

The self-styled anarchist movement partly traces its roots in the resistance to Greece's 1967-74 military dictatorship. The youths tend to espouse general anti-capitalist and antiestablishment principles, and have long-running animosity toward the police.