Chris Morris: "Desperate rescue efforts are well underway"

Reports from Istanbul and the cities of Adapazari and Izmit, say the quake, measuring 6.7 on the Richter scale, has caused about 100 deaths and injured more than 500.

The quake struck at 0302 local time (0002 GMT). As daylight breaks, the full extent of the damage caused is becoming apparent.

Turkish State Minister Hasan Gemici said; "According to information which has reached us, the death toll is now more than 100."

Buildings collapse

Multi-storeyed residential buildings have collapsed in Izmit, the city closest to the epicentre, and many people are believed to be trapped inside.

Fire crews have fought for several hours to bring under control a blaze at a major oil refinery on the outskirts of the city and power cuts have hit a wide area across one of Turkey's most heavily industrialised regions.

The shock was also felt in Istanbul, some 100km (65 miles) to the west of Izmit.

One resident in Istanbul e-mailed BBC News Online from the 18th floor of his office buliding. He said: "The most nervewracking 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 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.

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

Zafer Arapkirli left his home in Istanbul after he was woken by the blast

"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

The BBC's Chris Morris: "The emergency services are working in very dangerous circumstances"

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.

Most people were asleep at the time the tremor struck

The state news agency Anatolia has reported one person killed in Zonguldak on the Black Sea and another in the western town of Bursa, where at least 35 people were injured.

State radio said vehicles on the main highway linking Istanbul and Ankara slammed into each other during the earthquake.

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

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