Riots have erupted across Greece after police shot dead a teenage boy in the capital Athens, police officials said.

The rioting began in Athens soon after the shooting in the central Exarchia district, a regular flash-point of trouble between police and gangs of self-proclaimed anarchists.

Police fired tear gas at hundreds of stone-throwing youths, who burned dozens of cars, smashed shop windows and set fire to refuse containers.

In Thessaloniki, Greece's second largest city, hundreds of youths took to the streets after the news of the shooting was reported, and the protests soon spread to the northern cities of Komotini and Ioannina. Demonstrations also took place in the Cretan city of Hania.

"On behalf of the government and the prime minister, I express my sorrow for the incident and especially the death of the young boy," Interior Minister Prokopis Pavlopoulos said on private Mega TV.

"An investigation to clarify the situation has already begun. There will be an exemplary punishment and measures will be taken so that such a thing will not be repeated."

Two police officers were arrested and were being questioned over the incident, police sources said. Hundreds of people staged a march on police headquarters, where they were being held.

An Interior Ministry press officer said that Pavlopoulos had offered his resignation to Prime Minister Costas Karamanlis, but it had been rejected.

The shooting took place after a group of around six youths started pelting a police vehicle with stones. When one tried to throw a petrol bomb, a policeman shot him, said a police official, who declined to be identified.

The boy, who was not identified but was said to be 15 years old, was confirmed dead after being taken to hospital, police said.

Two witnesses, speaking on Mega TV, said they heard a verbal exchange between the police and the boys and then three shots. They said the boy died instantly.

The detained police officers have denied that they shot directly at the boy, police officials said. A forensic investigation is due to be carried out on Sunday