More than 500 people were killed and hundreds injured in Turkey and Syria, and the death toll is expected to rise.

Rescue workers and residents frantically searched for survivors under the rubble of buildings in multiple cities on both sides of the border.

The quake, felt as far away as Cairo, was centred north of the city of Gaziantep in an area about 95km (60 miles) from the Syrian border.

On the Syrian side of the border, the quake smashed opposition-held regions that are packed with some four million internally displaced people (IDP) from the long civil war. Many of them live in decrepit conditions with little healthcare. At least 11 people were killed in Atmeh and many more were buried in the rubble, Muheeb Qaddour, a doctor in the town, told The Associated Press news agency by telephone.

On the Turkish side, several big cities home to millions of Syrian refugees were in the affected area.

There were at least six strong aftershocks, and interior minister Suleyman Soylu urged people not to enter damaged buildings, citing risks.

The earthquake came as the region is experiencing a snowstorm that is expected to continue until Thursday.

Turkey sits on top of major fault lines and is frequently shaken by earthquakes.

Some 18,000 people were killed in powerful earthquakes that hit northwest Turkey in 1999.