Athens  - The Greek capital was ablaze and gripped by chaos late Monday and dozens of other cities were crippled for a third straight day by arson and looting in the worst riots in decades, triggered by the fatal police shooting of a teenager.

Thick black smoke, flames and tear gas engulfed central Athens as students set fire to several buildings including the offices of state airline Olympic Airways, the Foreign Ministry across from Parliament, a luxury department store, Greeces main law school and two bank headquarters.

As dusk fell on Athens, hooded youths could be seen setting fire to the city's massive Christmas tree and festive village and were reportedly making their way toward heavily guarded Parliament buildings.

Hooded protestors, mostly in their teens, clearly had control of the city by late Monday and were looting stores and taking anything that could be used as a weapon.

Dozens of shops, parked cars, banks and even luxury hotels had windows smashed as youths fought with riot police, who retaliated by beating protestors with batons and were able to arrest others.

Frightened pedestrians and tourists, many suffering breathing problems from the tear gas, ran for shelter.

The luxury hotel Athens Plaza in central Sytagma Square had all of its guests evacuated, reports said.

Earlier, more than 10,000 protestors from the Communist Party and other left-wing groups marched through the centre of Athens yelling anti-government slogans.

Clearly the worst riots Greece has seen in recent years began within hours of the fatal shooting of a teenager on Saturday night in the bohemian district of Exarhia in central Athens. Two police officers have been arrested and charged with manslaughter in the shooting.

Prime Minister Costas Karamanlis again appealed for calm after an emergency meeting Monday night with his ministers and top security officials, trying to find a way to break the chain of violence and destruction.

The interior minister emerged from the meeting saying the massive protests were unacceptable but insisted that police are doing all they can to protect lives and property.

With anger over economic hardships brewing for months and with many youths uncertain of their futures, the latest incident over the teenagers slaying could topple the unpopular conservative government.

Thousands of students, armed with fire bombs and stones, also clashed with police and smashed storefronts in the northern port city of Thessaloniki, and similar violence was reported in at least in eight other cities across Greece.

From the northern city of Veria to the central city of Trikala, rioters committed arsons and destroyed businesses and public buildings. A group of protestors even took over a television station in the western port city of Patras.

On Crete and the island of Corfu, massive riots took place with gangs of students torching banks and police stations.

Fire departments in both major Greek cities tried frantically to extinguish the flames, and in Athens firefighters were nearly burned to death when protestors set their truck on fire.

Hundreds of shopkeepers watched in dismay as their businesses were destroyed ahead of the busy Christmas shopping season, which retailers had hoped would make up for the financial crisis that has hit Greece.

The damage nationwide is estimated in the millions of euros.

Police have detained more than 50 people and 100 more were reported injured.

The head of the journalist federation, Panos Sombolos, said called it the worst rioting in Greece in his 30 years as a journalist.

Abroad, demonstrators attempted to take over the Greek embassies in London, Berlin and Cyprus. At the Greek embassy in London, protestors took down the Greek flag and put up a black and red anarchist flag in its place.

Public unrest has grown with the conservative government's austerity measures, with unions regularly demonstrating against privatizations, pension reforms and the cost of living. Twenty per cent of Greeks live below the poverty line.

"Enough of this government, which does not understand the problems of this country," main opposition Socialist leader George Papandreou said.

A new 24-hour general strike was called for Wednesday, and analysts predicted a new wave of riots to strike Greece. (dpa)