The 6.7 magnitude tremor left two men (from Turkey and Sweden) dead and 100 people hurt in Kos, a popular holiday destination among Britons.
Around 70 more were admitted to hospital in Bodrum, Turkey, with many injured as they attempted to escapte the tremor, which struck at 1.31am local time (11.30pm BST).
Many spent the night sleeping on beaches after fleeing their homes and hotels.
Aftershocks have plagued the area throughout the night, with some registering a magnitude of more than 4.0.
The earthquake was the second in the region to measure more than 6.0 on the richter scale this year. It was very shallow, just 6.2 miles below the seabed.
Pictures show damage to buildings in Kos and Bodrum, and flooding resulting from a small tsunami sparked by the quake.
Yiorgos Hadjimarkou, the head of the South Aegean region, has said that the primary concern “is safeguarding human life”.
This weekend is set to be among the busiest of the tourist season, with scores of Britons set to travel to Greece and Turkey, or already there.
For those affected, here is the latest travel advice.
A powerful 6.7 magnitude earthquake struck the Aegean sea, near Kos and Bodrum
The UK Foreign Office has advised holidaymakers in the affected areas to contact family and/or friends if it is safe to do so.
“You should be aware of the possibility of aftershocks, and follow the advice of the local authorities and/or your tour operator,” officials have advised.
Aftershocks “are happening and will happen”, Professor Ethymios Lekkas, the head of Greece’s anti-seismic protection organisation, told newsit.gr.
Turkey’s Disaster and Emergency Management Presidency (AFAD) head, Mehmet Halis Bilden, advised: “Our people should know that aftershocks are continuing, so they should refrain from entering damaged or vulnerable structures.”
Buildings in Bodrum have been left damaged by the earthquake
Parts of the area have been left flooded
Prof Lekkas described the tremors as “totally natural”, and said that Kos should expect to feel aftershocks for the foreseeable future.
Those who are travelling to and from the island imminently are advised to contact travel providers for updates, as flights and ferry services are being significantly disrupted as a result of the earthquake.
The port of Kos is one of the few structures damaged by the earthquake, leaving at least one ferry unable to dock.