The BBC's John Andrew: "It's the strongest quake in 20 years"

Three children are said to be among those who died in the tremor, which struck around 1500 local time (1200 GMT) and was followed by a series of strong aftershocks.

Many thousands of people are spending the night in the open, fearful of more tremors.

Athenians who were taking an afternoon siesta when the quake happened fled into the streets.

People were hit by falling glass, concrete and marble slabs. At least three were killed when a building collapsed in the northern working-class surburb of Menidi.

Journalist Robert McDonald: "Images from Turkey are still fresh in people's minds"

Emergency services are trying to free 70 people trapped under a collapsed detergent factory in the northern Metamorphosi suburb, one of the worst hit areas.

In the same area, as many as 50 workers were buried under the rubble of the collapsed showrooms of household appliance firm Fourlis.

A further 20 people were reported trapped under a flattened apartment building.

Reports say up to 100 buildings have been destroyed in the tremor.

"We heard a big thunder," said bus driver Argyris Karaiskos, who was in a city centre cafe. "Then there was a huge shake and there was panic."

A government spokesman said many people were trapped inside buildings and several dozen had been taken to hospital.

Greek Prime Minister Cosatas Simitis held an emergency cabinet meeting to deal with the crisis.

Damage near ancient ruins

Cracks appeared in buildings in the historic Plaka district, but there was no apparent damage to ancient sites, including the Acropolis and the Temple of Zeus.

Helena Smith: "My own balcony swayed back and forth for 10 seconds - it was terrifying"

The Athens Seismological Institute said the quake registered 5.9 on the Richter scale, and the epicentre was 20km (12.4 miles) north of the capital.

Experts said the seismic shift occurred 5 to 10km below the ground.

It is thought the epicentre was near to the proposed site for developments for the 2004 Olympics, which will be undoubtedly concern the authorities.

A series of aftershocks swayed buildings and prevented people from returning indoors.

The capital was declared an emergency danger zone and public offices and schools will be closed on Wednesday.

Government spokesman Dimitris Reppas said people made homeless by the quake would be put up in hotels and every homeless family would get 200,000 drachmas ($646.2) in emergency assistance.

The quake was also felt in western Turkey where a huge earthquake hit less than a month ago, killing at least 15,000 people.

Emergency aid is given to a man wounded by falling concrete

The Turkish disaster has drawn sympathy from EU countries - including its old enemy Greece, which has contributed to the emergency rescue operation.

Observers say it prompted a fundamental breakthrough in the attitude of the Greek Government to relations with Turkey, which has enabled the EU to begin forging closer ties and release significant sums of money.