The BBC's Rageh Omaar: "Many people are refusing to give up hope"

Buildings collapsed on sleeping residents as the tremor - which measured 6.8 to 7.0 on the Richter scale - rocked the major cities of Izmit, close to the epicentre, Istanbul and Adapazari.

A massive search and rescue operation is under way with military and civilian services co-ordinating their efforts.

Reports from the north-west of the country say survivors are scrambling desperately to try to rescue those trapped beneath the rubble of collapsed houses.

Hospitals have been overwhelmed. Makeshift medical centres have been set up on street corners and in ruined buildings.

Appearing close to tears on national television, Turkish Prime Minister Bulent Ecevit lamented the "huge loss" caused by the disaster.

Touring towns hit by the earthquake, he described it as the worst natural disaster he had ever seen and said that gargantuan efforts would be needed to rebuild.

International help

Offers of help have poured in from other countries. Neighbouring Greece says it is on standby to send a special catastrophe unit to the worst-affected areas.

Turkish minister responsible for rescue, Yayha Akkurt: "We are hoping for Western expert help"

Russia is flying rescue workers, medical specialists and search dogs to Turkey. Israel is organising emergency aid and Japan, Switzerland, Germany and the United Kingdom are sending specialist teams.

US Energy Secretary Bill Richardson, currently in Turkey for talks on the Caspian oil and gas pipeline, said the US had also offered assistance and sent a search-and-rescue team.

President Clinton said the US would do all it could to help.

Naval base hit

A Turkish naval base at Golcuk on the Marmara Sea was badly damaged with at least 20 sailors reported killed and 248 trapped under the rubble.

Mr Ecevit said many admirals and senior officers were among those trapped. Golcuk is one of the country's biggest naval bases with a large training centre.

The Anatolia news agency said the town was cut off to road traffic and covered in heavy smoke.

Power cuts

The quake struck at 0302 local time (0002 GMT) and many people are still trapped under mountainous debris.

A state of emergency has been declared in many provinces.

Turkish Interior Minister Saadettin Tantan told state television that a full assessment of the damage could not be made in any city and that many areas were without power.

Authorities urged residents not to return to their houses because of aftershocks. At least 200 tremors have been counted and it is feared that buildings will still collapse.

Cars filled the streets of Istanbul, home to some 10 million people, as residents tried to flee the area amid the aftershocks.

Fire crews fought for several hours to bring under control a blaze at a major oil refinery on the outskirts of Izmit.

Aftershocks

One resident in Istanbul e-mailed BBC News Online from the 18th floor of his office building. He said: "The most nerve-wracking part has been the aftershocks - at least 30 so far, some fairly strong.

John Watt of the International Federation of Red Cross and Red Crescent

"I keep my fingers crossed - and think of those in Izmit."

The timing of the quake means many people will have been asleep indoors when the quake struck, increasing the prospect of high casualties.

Television pictures from the area show dazed and bleeding people being rescued from the rubble by workers scraping at debris with their bare hands.

Many residents rushed from their homes after the first quake and have stayed in the open fearing further aftershocks.

"It was very powerful," said Izmit resident Mehmet Cankaya. "We were shaken out of our beds. Everyone is now out in the streets."

Crisis centre

In the capital, Ankara, where residents also felt the quake, officials at the prime minister's office have set up a crisis centre to co-ordinate emergency efforts.

However, fallen telephone lines and power cuts are hampering the rescue effort.

Last year a slightly less powerful earthquake killed more than 140 people and injured 1,500 near the southern city of Adana.

Our correspondent Chris Morris says that previous earthquakes have shown that many buildings are simply not strong enough to withstand the impact of tremors.

He says that Turkey experienced a building boom in recent years during which unscrupulous contractors built houses cheaply and quickly, despite the fact that Turkey lies on an active faultline.

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