Millions of people in the region, the most heavily populated in Turkey, have been spending the night in the open, frightened that further aftershocks will bring more devastation.

Latest reports say more than 2,000 people died and 13,000 were injured when the quake - measuring 6.7 on the Richter scale - struck an area around the industrial town of Izmit in the early hours of Tuesday morning.

The BBC's Paul Adams reports: "The devastation is total"

Officials say another 10,000 could still be trapped beneath the rubble.

Throughout the night, rescue workers - and ordinary people - continued their search for survivors, some digging through the debris with their bare hands. Correspondents say the death toll is likely to rise dramatically.

The fear of aftershocks has forced residents out of their homes

Turkey has declared a state of emergency in the disaster zone - which is the most heavily-populated area of Turkey - including the major cities of Istanbul and Adapazari .

It has also appealed for international help in locating and rescuing survivors still stuck in the rubble.

Offers of help have been pouring in, with Turkey emphasising that the greatest immediate need is for trained rescue teams. Israel, Germany the United States, Britain and Russia are sending groups of experts in search and rescue, and sniffer dogs.

(Click here to see a map of where the earthquake struck)

Survivors attempted to rescue those trapped beneath the rubble of collapsed houses, with many using their bare hands to tear away the debris.

Moments of triumph, such as when a toddler was lifted from ruins, apparently uninjured hours after the quake and passed to the arms of his father, provoked applause from watching crowds.

For those missing and still alive and already buried for 18 hours the next night and day will be crucial. Because of the hot weather, those trapped will have very little oxygen, and experience of previous earthquakes has shown they have little chance of surviving for more than 24 hours.

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

With the death toll rising remorselessly all day, state media reported 2,138 killed at 0200 GMT on Wednesday.

Worst natural disaster

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.

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.

Aftershocks

A state of emergency has been declared in many provinces.

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

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.

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.

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

The timing of the quake meant many people were asleep indoors when the quake struck, increasing the prospect of high casualties.

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

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

However, fallen telephone lines and power cuts have hampered the rescue effort.

Many buildings were simply not strong enough to withstand the impact of tremors.

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

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