A major earthquake of magnitude 7.9 killed more than 50 people in southern Turkey on Monday and was felt in Cyprus, Lebanon and Syria, collapsing dozens of buildings and triggering a search for survivors under the rubble in snowy streets.

Turkish authorities scrambled rescue teams and supply aircraft to the region around the city of Kahramanmaras, while declaring a "level 4 alarm" that calls for international assistance.

Early statements by officials suggested the death toll was at least 23 in Turkey's Malatya province, 17 in Sanliurfa, six in Diyarbakir and five more in Osmaniye. South across the border in Syria, state media said 42 had been killed.

"I have never felt anything like it in the 40 years I've lived," said Erdem, a resident of the Turkish city of Gaziantep, near the quake's epicentre, who declined to give his surname.

"We were shaken at least three times very strongly, like a baby in a crib."

It was still too dark to see the nature of the damage, he added.

"Everybody is sitting in their cars, or trying to drive to open spaces away from buildings," he said, speaking by telephone. "I imagine not a single person in Gaziantep is in their homes now."

The tremor lasted about a minute and shattered windows, according to a Reuters witness in Diyarbakir, 350 km (218 miles)to the east, where a security official said at least 17 buildings collapsed.

Local authorities said 16 structures collapsed in Sanliurfa and 34 in Osmaniye.

Broadcasters TRT and Haberturk showed footage of people picking through building wreckage, moving stretchers and seeking survivors in Kahramanmaras, where it was still dark.

"Our primary job is to carry out the search and rescue work and to do that all our teams are on alert," Interior Minister Suleyman Soylu told reporters.

The German Research Centre for Geosciences (GFZ) said the quake struck at a depth of 10 km (6 miles), while the EMSC monitoring service said it was assessing the risk of a tsunami.

The U.S. Geological Survey (USGS) reported a series of further earthquakes following the initial tremor, which it put at a magnitude of 7.8. There was a quake measuring 6.7 in Gaziantep and another of 5.6 in the city's Nurdag area.

Turkey's Disaster and Emergency Management Authority (AFAD) put the magnitude of the quake at 7.4 near Kahramanmaras and the larger city of Gaziantep, close to the Syrian border.

Syrian state media said a large number of buildings collapsed in the province of Aleppo, while a source in the Hama civil service said several buildings had collapsed there.

"Paintings fell off the walls in the house," said Samer, a resident of the capital, Damascus. "I woke up terrified. Now we're all dressed and standing at the door."

People in Damascus, and in the Lebanese cities of Beirut and Tripoli, ran into the street and took to their cars to get away from their buildings in case they collapsed, witnesses said.

Tremors were also felt overnight in Ankara, 460 km (286 miles) northwest of the epicentre, and in Cyprus, where police reported no damage.

The area is regularly hit by strong earthquakes.

"The earthquake struck in a region that we feared. There is serious widespread damage," Kerem Kinik, the chief of the Turkish Red Crescent relief agency, told Haberturk, issuing an appeal for blood donations.