The Foreign Office has warned tourists travelling to Greece and Turkey that flights and ferry services are being "significantly disrupted".
Two people have died and more than 120 have been injured in an early morning earthquake off the coast of Greek islands and Turkey.
The quake, said to have been up to a magnitude of 6.7, struck south of the Turkish city of Bodrum and east of the Greek island of Kos - areas popular with British holidaymakers.
Buildings on Kos were damaged by the tremors, which prompted a small tsunami, flooding parts of the island.
Tourists had to flee their hotel rooms when the quake hit at around 1.30am, and have been experiencing aftershocks throughout the night.
The Foreign Office has urged tourists in the affected area to contact friends and family to tell them they are safe, if it is safe to do so.
A statement from the Foreign Office said: "You should be aware of the possibility of aftershocks, and follow the advice of the local authorities and/or your tour operator.
"Flights and ferry services are being significantly disrupted as a result of the earthquake. Please contact your airline, ferry company or tour operator for updates to services."