A powerful earthquake hit Greece and Turkey on Friday, causing buildings to collapse and a sea surge that flooded streets in the Turkish resort city of Izmir.

Greek public television said the quake also caused a mini-tsunami on the eastern Aegean Sea island of Samos, damaging buildings.

The US Geological Survey said the 7.0 magnitude quake was registered 14 kilometres (8.6 miles) off the Greek town of Karlovasi on Samos.

The Turkish government's disaster agency reported a lower magnitude of 6.6 for the quake while Greece's seismological agency said it measured 6.7.

Images from Izmir showed collapsed buildings and dazed people trying to make their way through rubbled piled high on the streets.

"So far, we have received information about six collapsed buildings" in Izmir province, which incudes the city, Turkish Interior Minister Suleyman Soylu said on Twitter.

"Some of our fellow citizens are stuck in the rubble," said Environment Minister Murat Kurum, adding that he knew of five collapsed buildings.

The city's mayor Tunc Soyer told CNN Turk he had information about the collapse of 20 buildings.

Images on social media showed water rushing through the streets of Izmir from an apparent sea surge.

Thick white plumes smoke rose from various parts of the city where buildings had collapsed.

Aerial footage on Turkey's NTV television showed entire city blocks turned to rubble.

TRT television showed rescuers being helped by residents and police using chainsaws as they tried to force their way through the rubble of a seven-floor building that had collapsed.

Rescuers called for silence for signs of any survivers, clearing boulders and other debris in a human chain.

CNN Turk showed one woman being pulled out alive.

Turkish President Recep Tayyip Erdogan tweeted that he was ready to help "with all the means available to our state".

- 'It was chaos' -

On the Greek island of Samos, near the quake's epicentre, people rushed out into the streets in panic.

"The walls of some houses have crumbled and several buildings are damaged," the island's deputy mayor Michalis Mitsios was quoted as saying by public broadcaster ERT.

"It was chaos," added fellow deputy mayor Giorgos Dionysiou. "We have never experienced anything like this."

The Greek civil protection agency told Samos's residents in a text message to "stay out in the open and away from buildings".

The island's airport was also closed as a precaution.

Greece and Turkey are both situated in one of the world's most active earthquake zones.

In 1999, a 7.4 magnitude earthquake struck Turkey's northwest, killing more than 17,000 people, including 1,000 in Istanbul.

Another quake in 2011 in the southeastern province of Van resulted in more than 600 deaths.

In Greece, the last deadly quake killed two people on the island of Kos, near Samos, in July 2017.