Hundreds of high school and university students joined self-styled anarchists in throwing everything from fruit and coins to rocks and Molotov cocktails at police and attacked police stations throughout the day. Police said some rioters were armed with crossbows, knives and swords.
"Cops! Pigs! Murderers!" protesters screamed at riot police.
Police said early Tuesday that 89 people had been arrested in Athens for attacking police officers, vandalism and looting and 79 more were being questioned about possible involvement in the rioting. The fire service said it responded to more than 200 blazes in central Athens on Monday, about half of them in buildings and the rest in cars and trash bins used as barricades.
Officials said violence eased early Tuesday, although some clashes continued in central Athens, dozens of masked youths were said to be holed up in a university building in the city center, but Greece bars police from entering university grounds.
Prime Minister Costas Karamanlis, who has already faced a growing number of sometimes violent demonstrations, held an emergency Cabinet meeting Monday night.
"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. "The state will protect society."
But his calls for calm went unheeded. The widely televised scenes of destruction were a new blow to an increasingly unpopular conservative government that has been rocked by financial scandals and retains a razor-thin majority of just one seat in the 300-member Parliament.
"In the streets today, a whole generation mourns," George Papandreou, leader of the opposition socialists, said in calling for a peaceful demonstration in Athens on Tuesday to protest "against state violence, against violence towards our fellow people."
Amid the riots, about 10,000 protesters from the Communist Party of Greece and another left-wing party marched through the center of Athens to protest the teenager's death.
Rioting raged in about a dozen cities, from Thessaloniki in the north to cities in Crete and the holiday island of Corfu. In Athens, rioters burned the capital's huge 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 "Oh 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.
The four-story Olympic Airways office building in central Athens was completely burned as were a Greek bank and dozens of other stores on Athens' central streets.
Rioters 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 dozens of fires. In Athens, rioters surrounded a 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.
Interior Minister Prokopis Pavlopoulos described the riots as "unacceptable" but insisted police were responding as well as they could to the widespread destruction to property.
"Not a single life is in danger. ... That is very important," Pavlopoulos said after the two-hour emergency Cabinet meeting.
"Human life is top priority. Property comes next."
"Under no circumstances will the government tolerate what is happening," he said.
Riots first erupted across the country Saturday after 15-year-old Alexandros Grigoropoulos was fatally shot by a police officer in Athens' often volatile Exarchia district.
The circumstances surrounding the shooting were unclear, but the two officers involved were arrested. One was charged with murder and the other as an accomplice. A coroner's report said the youth was shot in the chest.
The funeral was set for Tuesday afternoon. 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.
Abroad, demonstrators raised banners at the Greek Embassy in London and the black-and-red anarchist flag at the Greek consulate in Berlin.
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 that was attacked and ruined said rioters didn't think about ordinary people like her.
"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.
