The death toll of a devastating earthquake in southern Turkey and Syria has jumped to more than 7800 people as rescuers work against time in harsh winter conditions to dig survivors out of the rubble of collapsed buildings.

As the scale of the disaster became ever more apparent, the death toll looked likely to rise considerably – while satellite images revealed the extent of some of the devastation from this week’s tremors.

One United Nations official said thousands of children might have died.

“It’s like we woke up to hell,” said Osman Can Taninmis, whose family members were still beneath the rubble in Hatay, Türkiye’s hardest-hit province.

“We can’t respond to absolutely anything. Help isn’t coming, can’t come. We can’t reach anyone at all. Everywhere is destroyed.”

Turkish President Tayyip Erdogan declared a state of emergency in 10 provinces. But residents in several damaged Turkish cities voiced anger and despair at what they said was a slow and inadequate response from the authorities to the deadliest earthquake to hit Turkey since 1999.

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Monday’s magnitude 7.8 quake, followed hours later by a second one almost as powerful, toppled thousands of buildings including hospitals, schools and apartment blocks, injured tens of thousands and left countless people homeless in Turkey and northern Syria.

Rescue workers struggled to reach some of the worst-hit areas, held back by destroyed roads, poor weather and a lack of resources and heavy equipment.

Some areas were without fuel and electricity.

With little immediate help at hand, residents picked through rubble sometimes without even basic tools in a desperate hunt for survivors.

Doctors Without Borders executive director Avril Benoit said search and rescue was the most urgent need on the ground. The humanitarian group has about 500 staffers in Syria – including some of who have lost their own family members in the earthquakes.

“The ideal window is to be able to bring people out within 48 hours,” Ms Benoiît told CNN.

“It’s highly risky and the likelihood of finding people alive diminishes and then from there, you’ve got people with catastrophic injuries. We’ve seen time and again with earthquakes that that is not only a need for trauma care, but then it’s infection control, it’s management of their postoperative care, rehabilitation, reconstruction of the hospitals themselves.”

Ms Benoit said babies were still being born – including one rescued from under the rubble still attached to her dead mother by her umbilical cord. Doctors Without Borders has redeployed staff from other medical units to assist evacuated mothers and newborns.

“Sometimes you’re evacuating to facilities, other hospital structures that frankly don’t necessarily have the integrity – structurally – that you would want, ideally,” Ms Benoit said.

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Aid officials voiced particular concern about the situation in Syria, already afflicted by a humanitarian crisis after almost 12 years of civil war.

Mr Erdogan declared 10 Turkish provinces a disaster zone and imposed a state of emergency for three months. It will permit the government to bypass parliament in enacting laws and to limit or suspend rights and freedoms.

The government would open up hotels in the tourism hub of Antalya to temporarily house people affected by the quakes, said Mr Erdogan, who faces a national election in three months.

The death toll in Turkey rose to 5894, Vice President Fuat Oktay said, with more than 34,000 were injured.

In Syria, the toll was at least 1932, according to the government and a rescue service in the insurgent-held north-west.

The Syrian Civil Defence, known as the “White Helmets”, said at least 2600 people had been injured. Numbers were “expected to rise significantly due to the presence of hundreds of families under the rubble”, the group added.

“Our teams continue search and rescue operations amid difficult circumstances,” it said, describing a tally of more than 400 collapsed buildings, more than 1300 partially collapsed buildings and thousands of others that were damaged by the early morning quake.

Turkish authorities say some 13.5 million people were affected in an area spanning roughly 450 kilometres from Adana in the west to Diyarbakir in the east, and 300 kilometres from Malatya in the north to Hatay in the south.

Syrian authorities have reported deaths as far south as Hama, some 250 kilometres from the epicentre.

“It’s now a race against time,” World Health Organisation Director-General Tedros Adhanom Ghebreyesus said in Geneva.

“Every minute, every hour that passes, the chances of finding survivors alive diminishes.”

Across the region, rescuers toiled night and day as people waited in anguish by mounds of rubble clinging to the hope that friends, relatives and neighbours might be found alive

In Antakya, capital of Hatay province bordering Syria, rescue teams were thin on the ground and residents picked through debris themselves. People pleaded for helmets, hammers, iron rods and rope.

More than 12,000 Turkish search and rescue personnel are working in the affected areas, along with 9000 troops. More than 70 countries offered rescue teams and other aid.

But the sheer scale of the disaster is daunting.

Turkey’s Disaster and Emergency Management Authority said 5775 buildings had been destroyed in the quake and 20,426 people had been injured.

Two United States Agency for International Development teams with 80 people each and 12 dogs were to arrive in Turkey early on Wednesday and head to the south-eastern province of Adiyaman to focus on urban search and rescue.

UNICEF spokesperson James Elder said in Geneva the earthquake “may have killed thousands of children”.

Syrian refugees in north-west Syria and in Turkey were among the most vulnerable people affected, Mr Elder said.

In the Syrian city of Hama, mosques opened their doors to families whose homes were damaged.

The Syrian state news agency SANA said at least 812 people were killed in the government-held provinces of Aleppo, Latakia, Hama, Idlib and Tartous.

At least 1120 people were killed in Syria’s opposition-held northwest with the toll expected to “rise dramatically”, the White Helmets rescue team said.

-with AAP