More than 1,500 people were killed and thousands injured on Monday when an earthquake struck central Turkey and northwest Syria, collapsing apartment blocks and heaping more destruction on Syrian cities already devastated by years of war.

The magnitude 7.8 quake, which hit in the early darkness of a winter morning, was the worst to hit Turkey this century. It was also felt in Cyprus and Lebanon.

Rescue workers operating in bitter winter weather pulled casualties from rubble across the region. The operation is being hampered by severe aftershocks.

The European Mediterranean Seismological Centre (EMSC) said a second tremor of 7.7 magnitude had struck Central Turkey.

Strong aftershocks were also reported elsewhere in Turkey and Syria.

Turkish President Tayyip Erdogan said 912 people were killed, 5,383 injured, and 2,818 buildings had collapsed in the first quake.

Erdogan said he could not predict how much the death toll would rise as search and rescue efforts continued.

In Syria, already wrecked by more than 11 years of civil war, the government and rescue workers said at least 560 people had been killed and 1,042 injured. In the Syrian rebel-held northwest, rescuers said 147 people had died.

In Diyarbakir, Reuters journalists saw dozens of rescue workers searching through a mound of debris, all that was left of a big building, hauling off bits of wreckage as they looked for survivors. Occasionally they raised their hands and called for quiet, listening for sounds of life.

Men carried a girl wrapped in blankets from a collapsed building in the city.

"We woke up to a big noise and severe shaking. There were two aftershocks right after that," said Meryem, 29, from the southeastern Turkish city of Kahramanmaras, near the epicentre.

"I was so scared, thought it will never stop. I took some things for my one-year old son and left the building."

Footage circulated on Twitter showed two neighbouring buildings collapsing one after the other in Syria's Aleppo, filling the street with billowing dust. Two residents of the city, which has been heavily damaged in the war, said the buildings had fallen in the hours after the quake.

Aleppo health director Ziad Hage Taha told Reuters wounded people were "arriving in waves".

Syrian state television showed footage of rescue teams searching for survivors in heavy rain and sleet.

In Afrin, a Syrian opposition-held town, rescue workers from the White Helmets response organization searched in the pre-dawn darkness for people trapped in a collapsed building. Using only torchlight, they pulled a man in a white vest and dark trousers from the rubble, carrying him away for treatment.

In the border town of Azaz - another rebel-held area - a rescue worker carried a toddler from a damaged building.

"It was like the apocalypse," said Abdul Salam al Mahmoud, a Syrian contacted by Reuters from the town of Atareb. (Reuters/AFP)