The 7.8-magnitude earthquake, which struck just before sunrise during a harsh winter, was Turkey's worst this century.

 Rescuers in Turkey and Syria dug with their bare hands Tuesday night for survivors amid the rubble of thousands of houses that collapsed in several powerful earthquakes.

The number of confirmed cases in both countries rose to more than 4,300 after the tremors near the Turkey-Syria border, the largest of which reached a magnitude of 7.8.

Turkish and Syrian disaster response teams report more than 5,600 buildings have collapsed in several cities, including many multi-storey buildings that were full of sleeping residents when the first earthquake hit.

In the town of Kahramanmaras in southeastern Turkey, those who saw it with their own eyes struggled to understand the scale of the disaster.

"We thought it was the apocalypse," said Melisa Salman, a 23-year-old journalist. "It's the first time we've had something like this."

Turkey's aid agency AFAD said on Tuesday there were now 2,921 deaths in the country alone, bringing the total confirmed to 4,365.

These numbers are feared to rise significantly, and the World Health Organization estimates that up to 20,000 people may die.

In Gaziantep, a Turkish city home to many refugees from Syria's decade-long civil war, rescuers digging through the rubble screamed, screamed and sought safety as another building collapsed nearby without warning.

The first earthquake was so large, it was felt as far as Greenland, and its impact was so large that it triggered a global response.

Many countries from Ukraine to New Zealand have pledged to send aid, although heavy rains and extreme heat have slowed the response.

In the city of Sanliurfa in southeastern Turkey, rescuers worked late into the night trying to find survivors from the rubble of a collapsed seven-story tower block. "There is a family I know under the rubble," said Omer El Cuneyd, a 20-year-old Syrian student.

"Until 11 o'clock in the morning or afternoon, my friend is still answering the phone. But he didn't respond anymore. He was there."

Even though it was cold outside, the frightened villagers spent the night in the streets, huddled around the fire for warmth. Mustafa Koyuncu took his wife and five children into their car and was afraid to move.

"We can't go home," the 55-year-old told AFP. "Everybody's scared."

Some of the worst damage occurred near the epicenter of the earthquake between Kahramanmaras and Gaziantep, where the ruins of all the towns under the snow are piling up.

Monday's first earthquake struck at 4:17 a.m. (0117 GMT) at a depth of about 18 kilometers (11 miles) near the Turkish city of Gaziantep, home to about two million people, the US said. More than 14,000 people were injured in Turkey, the disaster management agency said, while Syria said at least 3,411 people were injured.

Officials said three airports had been rendered inoperable, disrupting the delivery of life-saving aid. The cold wave covered major roads in the area with ice and snow.

Most of the earthquake-affected areas of northern Syria have been devastated by years of war and airstrikes by the Syrian and Russian forces have destroyed homes, hospitals and clinics.

The conflict is shaping the emergency response, with Syria's UN envoy Bassam Sabbagh apparently determined to reopen crossings that would allow aid to reach areas controlled by rebel groups.

Syria's health ministry reported damage in the provinces of Aleppo, Latakia, Hama and Tartous, where Russia is leasing naval facilities.

Even before the disaster, the buildings in Aleppo - the business center of Syria before the war - were often collapsing due to broken infrastructure, which suffered from the lack of wartime maintenance.

Authorities shut off gas and electricity throughout the region as a precaution, and schools closed for two weeks.

The United Nations' cultural agency, UNESCO, has expressed concern over the extensive destruction of two cities on its heritage list, Aleppo in Syria and Diyarbakir in Turkey.

In the prison of many members of the Islamic State in northwestern Syria, prisoners broke out after the earthquake, and at least 20 people escaped, a source told AFP.

The United States, the European Union and Russia all immediately sent their complaints and assistance.

President Joe Biden has promised Turkish President Recep Tayyip Erdogan and the United States will send "all" the aid needed to aid recovery from the massive earthquake.

Ukrainian President Volodymyr Zelensky has also offered to provide "necessary aid" to Turkey, whose warships are helping Kyiv fight Russian aggression. Turkey is one of the most active seismic regions in the world.

The country's last 7.8 earthquake was in 1939, when 33,000 people died in the eastern province of Erzincan. Turkey's Duzce region was hit by a magnitude 7.4 earthquake in 1999, which killed more than 17,000 people.

Experts have long warned that a major earthquake could devastate Istanbul, a metropolis of 16 million people filled with war-torn buildings.