A powerful earthquake of magnitude 7.0 has struck off Turkey's Aegean coast, north of the Greek island of Samos, officials said.
The tremor, about 17km (11 miles) off the coast of western Izmir province, was felt in Athens and Istanbul, the US Geological Survey (USGS) said.
The European-Mediterranean Seismological Centre said the quake had a preliminary magnitude of 6.9, with an epicentre 13 kilometres north northeast of the Greek island of Samos.
Turkey's President Reccep Tayyip Erdogan tweeted: "Get well soon İzmir."
"With all the means of our state, we stand by our citizens affected by the earthquake. We took action to start the necessary work in the region with all our relevant institutions and ministers," Erdogan said.
Four causalities have been confirmed so far while images from the Turkish city of Izmir showed buildings that had collapsed.
The video showed flooded streets in the city, apparently caused by a small tsunami following the earthquake.
Local media reported 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.
Turkey’s health minister Fahrettin Koca said on Friday that four people had died in the incident, while video footage on social media showed buildings in the Turkish city of Izmir had been seriously damaged.
“Unfortunately, four of our citizens died in the earthquake in Izmir. In total, 120 citizens were affected by the earthquake,” Mr Koca said.
Bugra Gokce, secretary general of the Izmir Metropolitan Municipality, told Turkish news channel NTV that several houses in the city had been destroyed in the tremor.