A 7.8-magnitude earthquake hit Turkey and Syria early on Monday, killing nearly 200 people, levelling buildings while many were still asleep, and sending tremors that were felt as far away as the island of Cyprus and Egypt.

The emergency service in Turkey put the initial death toll at 76, although it threatened to climb substantially higher because the night-time disaster had flattened dozens of apartment blocks across major cities.

At least 119 people also died in government-controlled parts of Syria, as well as the northern areas held by pro-Turkish factions, according to the health ministry and a local hospital.

Television images showed shocked people in Turkey standing in the snow in their pyjamas, watching rescuers dig through the debris of damaged homes.

The quake struck at 04:17 am local time (0117 GMT) at a depth of about 17.9 kilometres (11 miles) near the Turkish city of Gaziantep, which is home to around two million people, the US Geological Survey said.

Turkey's AFAD emergencies service centre put the first quake's magnitude at 7.4, adding that it was followed by more than 40 aftershocks.

The earthquake was one of the most powerful to hit the region in at least a century, affecting southeastern parts of Turkey that are home to millions of refugees from Syria and other war-torn parts of the world.

Turkish President Recep Tayyip Erdogan, who will be under intense pressure to oversee an effective response to the disaster heading to a tightly-contested May 14 election, conveyed his sympathies and urged national unity.

"We hope that we will get through this disaster together as soon as possible and with the least damage," the Turkish leader tweeted.

US National Security Advisor Jake Sullivan said Washington was "profoundly concerned".

"We stand ready to provide any and all needed assistance," Sullivan said.

'People under rubble'

The earthquake struck a restive, predominantly Kurdish area of Turkey near Syria, a country gripped by more than a decade of violence that has killed hundreds of thousands and displaced millions of people.

Images on Turkish television showed rescuers digging through the rubble of levelled buildings in the city of Kahramanmaras and neighbouring Gaziantep, where entire sections of cities were destroyed.

A fire lit up the night sky in one image from Kahramanmaras, although its origin remained unclear.

Buildings also crumbled in the cities of Adiyaman, Malatya and Diyarbakir, where AFP reporters saw panicked people rush out on the street.

Kahramanmaras Governor Omer Faruk Coskun said it was too early to estimate the death toll because so many buildings were destroyed.

"It is not possible to give the number of dead and injured at the moment because so many buildings have been destroyed," Coskun said. "The damage is serious."

A famous mosque dating back to the 13th century partially collapsed in the province of Maltaya, where a 14-story building with 28 apartments also collapsed.

In other cities, rescuers sounded anguished as they struggled to reach survivors trapped under the debris.

"We hear voices here -- and over there, too," one rescuer was overheard as saying on NTV television in front of a flattened building in the city of Diyarbakir.

"There may be 200 people under the rubble."

'Biggest earthquake'

The Syrian health ministry reported damage across the provinces of Aleppo, Latakia, Hama and Tartus, where Russia is leasing a naval facility.

AFP correspondents in northern Syria said terrified residents ran out of their homes after the ground shook.

Raed Ahmed, who heads Syria's National Earthquake Centre, told pro-government radio that this was "historically, the biggest earthquake recorded in the history of the centre".

Naci Gorur, an earthquake expert with Turkey's Academy of Sciences, urged local officials to immediately check the region's dams for cracks to avert potentially catastrophic floodings.

Turkey is in one of the world's most active earthquake zones.

The Turkish region of Duzce suffered a 7.4-magnitude earthquake in 1999 -- the worst to hit Turkey in decades.

That quake killed more than 17,000 people, including about 1,000 in Istanbul.

Experts have long warned a large quake could devastate Istanbul, which has allowed widespread building without safety precautions.

A magnitude-6.8 quake hit Elazig in January 2020, killing more than 40 people.

And in October that year, a magnitude-7.0 quake hit Turkey's Aegean coast, killing 114 people and wounding more than 1,000.