An earthquake beneath the sea shook northern Greece and western Turkey today, with more than two dozen injuries reported on a Turkish island.

In Istanbul and other parts of Turkey residents fled homes in panic after the quake struck.

The private Dogan news agency said it caused damage to some old houses on the island of Gokceada, off Turkey's northern Aegean coast, and 30 people were taken to a hospital with minor injuries.

The quake struck south-west of the Greek island of Samothraki, 210km east of Thessaloniki and 296km north-east of the capital, Athens at 12.25pm local time (0925 GMT). It was also close to the Turkish island of Gokceada and the Greek island of Lemnos.

A duty officer at the Lemnos police precinct said a female British tourist was slightly injured at the airport when part of the ceiling fell, but she was treated at the scene and did not need to go to hospital. No other damage or injuries had been reported.

The Institute of Geophysics at the Aristotle University of Thessaloniki said the quake had a magnitude of 6.3. The US Geological Survey initially reported a magnitude of 6.4, which was later revised to 6.9.

There were discrepancies as to the depth, as well. The USGS reported a depth of 10 kilometres but the Athens Geodynamics Institute reported it as 27 kilometres.

The tremor was widely felt, including in Thessaloniki, the west coast of Turkey and as far away as Bulgaria and Istanbul. Several strong aftershocks, of yet undetermined magnitude, have also taken place.

"The earthquake has occurred in an area with especially high seismic activity, which, in the past, has given earthquakes up to 7 magnitude (in 1982)," Manolis Skordilis, of the Institute of Geophysics, told the Associated Press.

"We are currently analysing the aftershocks and are on alert," he added.