HATAY - Rescuers in Turkey and Syria dug with their bare hands through the freezing night Tuesday hunting for survivors among the rubble of thousands of buildings felled in a series of violent earthquakes.
The confirmed death toll across the two countries has soared above 4,300 after a swarm of strong tremors near the Turkey-Syria border -- the largest of which measured at a massive 7.8-magnitude.
Turkish and Syrian disaster response teams report more than 5,600 buildings have been flattened across several cities, including many multi-storey apartment blocks that were filled with sleeping residents when the first quake struck.
In the city of Kahramanmaras in southeastern Turkey, eyewitnesses struggled to comprehend the scale of the disaster.
"We thought it was the apocalypse," said Melisa Salman, a 23-year-old reporter. "That was the first time we have ever experienced anything like that."
Turkey's relief agency AFAD on Tuesday said there were now 2,921 deaths in that country alone, bringing the confirmed tally to 4,365.
There are fears that toll will rise inexorably, with World Health Organization officials estimating up to 20,000 may have died.
In Gaziantep, a Turkish city home to countless refugees from Syria's decade-old civil war, rescuers picking through the rubble screamed, cried and clamoured for safety as another building collapsed nearby without warning.
The initial earthquake was so large it was felt as far away as Greenland, and the impact is big enough to have sparked a global response.
Dozens of nations from Ukraine to New Zealand have vowed to send help, although freezing rain and sub-zero temperatures have slowed the response.
In the southeastern Turkish city of Sanliurfa, rescuers were working into the night to try and pull survivors from the wreckage of a seven-storey building that had collapsed.
"There is a family I know under the rubble," said 20-year-old Syrian student Omer El Cuneyd.
"Until 11:00 am or noon, my friend was still answering the phone. But she no longer answers. She is down there."
Despite freezing temperatures outside, terrified residents spent the night on the streets, huddling around fires for warmth.
Mustafa Koyuncu packed his wife and their five children into their car, too scared to move.
"We can't go home," the 55-year-old told AFP. "Everyone is afraid."
Some of the heaviest devastation occurred near the quake's epicentre between Kahramanmaras and Gaziantep, where entire city blocks lay in ruins under gathering snow.
- 'Apocalypse' -
Monday's first earthquake struck at 4:17am (0117 GMT) at a depth of about 18 kilometres (11 miles) near the Turkish city of Gaziantep, which is home to around two million people, the US Geological Survey said.
More than 14,000 people have so far been reported injured in Turkey, the disaster management agency said, while Syria said at least 3,411 people were injured.
Officials said three major airports have been rendered inoperable, complicating deliveries of vital aid.
A winter blizzard has covered major roads into the area in ice and snow.
Much of the quake-hit area of northern Syria has already been decimated by years of war and aerial bombardment by Syrian and Russia forces that destroyed homes, hospitals and clinics.
The conflict is already shaping the emergency response, with Syria's envoy to the United Nations Bassam Sabbagh seemingly ruling out reopening border crossings that would allow aid to reach areas controlled by rebel groups.
The Syrian health ministry reported damage across the provinces of Aleppo, Latakia, Hama and Tartus, where Russia is leasing a naval facility.
Even before the tragedy, buildings in Aleppo -- Syria's pre-war commercial hub -- often collapsed due to the dilapidated infrastructure, which has suffered from a lack of wartime oversight.
Officials cut off natural gas and power supplies across the region as a precaution, also closing schools for two weeks.
The UN cultural agency UNESCO expressed fears over heavy damage in two cities on its heritage list -- Aleppo in Syria and Diyarbakir in Turkey.
At a jail holding mostly Islamic State group members in northwestern Syria, prisoners mutinied after the quakes, with at least 20 escaping, a source at the facility told AFP.
The United States, the European Union and Russia all immediately sent condolences and offers of help.
President Joe Biden promised his Turkish counterpart Recep Tayyip Erdogan that the United States will send "any and all" aid needed to help recover from a devastating earthquake.
Ukrainian President Volodymyr Zelensky also offered to provide "the necessary assistance" to Turkey, whose combat drones are helping Kyiv fight the Russian invasion.
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, when more than 17,000 people died.
Experts have long warned a large quake could devastate Istanbul, a megalopolis of 16 million people filled with rickety homes.
burs-arb/cwl
By Bulent Kilic