More than 250 people were wounded on Saturday when a 6.9 magnitude undersea earthquake sparked panic in northwestern Turkey.

Television footage showed hundreds of terrified residents fleeing buildings in several Turkish towns after the quake hit at 0925 GMT.

Turkey's emergency services department said 266 people were wounded, most of them in the panic that followed the quake. A hospital was also damaged.

"The quake caused some damage to homes, but no serious destruction has been reported," said department official Murat Nurlu.

The US Geological Survey said the quake's epicentre was under the Aegean Sea off the Greek island of Lemnos, and put its magnitude at 6.9.

There were no reports of any major damage or casualties on the island, although local police said a British tourist was slightly injured when part of the ceiling at Lemnos airport collapsed.

The tremor was felt in the Bulgarian capital Sofia and in Istanbul, a city of 15 million people.

Istanbul is in the area of Turkey that sits on the active North Anatolian fault and was hit by two strong quakes in 1999 that killed around 200,000 people.

Earthquakes occur frequently in Greece. In January, thousands of people were left homeless by a quake on the Ionian island of Cephalonia, in the west of the country.