The BBC's Chris Morris: "Desperate rescue efforts are underway"

Latest reports say 120 people have died and more than a thousand have been injured.

The casualty figures are expected to increase as an unknown number of people are trapped under the rubble of collapsed buildings.

"We are face-to-face with a new disaster," said Turkish President Suleyman Demirel.

The tremor measured 7.2 on Richter scale, the Kandilli Seismic Institute in Istanbul said, revising upwards an earlier estimate of 6.5.

Local people said some 30 buildings had collapsed.

The quake also set off explosions in the province of Bolu.

The quake, which struck at 1859 local time (1659 GMT), had its epicentre in the town of Duzce, some 170km (115 miles) east of Istanbul.

It was followed by five aftershocks measuring more than five on the Richter scale, according to the Kandilli Seismic Institute in Istanbul.

Reports said casualties in Duzce had to be treated in the garden of the local hospital, as the building had to be evacuated because it was unsafe.

A makeshift operating theatre was set up with lighting provided by a generator.

Hundreds of people gathered in Duzce's park, huddling around makeshift fires as temperatures fell to 3 C by the early morning.

Explosions

Chris Morris in Ankara: "No-one can believe it's happened again"

In nearby Bolu, the earthquake set off explosions in buildings, which triggered fires, the town's police chief, Ugur Gur, said.

He said the road to Istanbul was severed during the quake and called for urgent medical aid from the capital, Ankara.

The tremor, which was felt across western Anatolia, came just a day after one person was killed and 171 injured by a quake measuring 5.7 on the Richter scale.

Thursday's tremor was centered on the town of Sapanca in Sakarya province which is still recovering from the massive quake on 17 August that killed at least 17,000 people.

Outside help

Rescue teams from abroad were preparing to travel to Turkey early on Saturday to help in the search for survivors.

Rescue workers bring out another casualty

Germany, Greece, France, Israel and the UK are among about a dozen countries which have offered help.

The latest earthquakes come as the city of Istanbul prepares to host next week's summit of the Organisation for Security and Co-operation in Europe.

US President Bill Clinton and his Russian counterpart Boris Yeltsin are expected to attend.