Initial estimates by the European Mediterranean Seismological Centre (EMSC) put the magnitude of the earthquake, which struck north of the eastern island of Samos at around 11:50 GMT, at 6.7.
There were no immediate reports of casualties on Friday but video footage on social media showed buildings in the Turkish city of İzmir had been seriously damaged.
Disturbing footage of a building collapsing after the earthquake #deprem pic.twitter.com/pV3FmbDkBq
— Abdullah Tanriverdi (@Abdullahtnrvdi) October 30, 2020
#izmir #deprem #earthquake At least 20 buildings have collapsed after quake in Aegean Sea pic.twitter.com/x3sQZXftrT
— Baba Umar (@BabaUmarr) October 30, 2020
Videos also showed flooded streets in the city, apparently caused by a small tsunami following the earthquake.
İzmir'de #deprem sonrası küçük çaplı tsunami oluşmaya başladı pic.twitter.com/VDl9QcH9E9
— Ata Benli (@atabenli) October 30, 2020
Suleyman Soylu, Turkey's interior minister, wrote on Twitter that six buildings had collapsed in two districts of Izmir province.
However, the city's mayor Tunc Soyer told CNN Turk that about 20 buildings had collapsed on Friday.
Izmir, which is the country's third-biggest city, contains about 4.5 million residents.
Turkey's Disaster and Emergency Management Presidency said the earthquake was centered in the Aegean Sea at a depth of 16.5 kilometres (10.3 miles).
Local media added that the tremor was felt across the regions of Aegean and Marmara, where Istanbul is located.
Meanwhile, Greek media said residents of Samos and other islands fled their homes, while some rockfalls were reported.
Residents of Samos, which has a population of about 45,000 people, have been urged to stay away from coastal areas, Eftyhmios Lekkas, head of Greece's organisation for anti-seismic planning, told the country's Skai TV.
"It was a very big earthquake, it's difficult to have a bigger one," Mr Lekkas said.
High tidal wave warnings have also been put in place in Samos.




Comment: Update: An AFP report carried by Channels Television on October 31 states: Update 2: AP reports on November 1: Update3: Anadolu Agency reports on November 2: