The World Health Organization has warned that the death toll from a powerful earthquake that struck southeastern Turkey near the Syrian border could rise eightfold.
The death toll, currently more than 3,400, has increased rapidly since the first quake struck early Monday morning.
About 12 hours later, a second strong earthquake hit north.
Rescuers comb mountains of rubble in freezing and icy conditions to find survivors.
Countries around the world are sending support to help with the rescue effort, including specialized teams, sniffer dogs and equipment.
The US Geological Survey said the 7.8-magnitude quake occurred at 04:17 local time (01:17 GMT) at a depth of 17.9 kilometers (11 miles) near the city of Gaziantep.
Seismologists said that the first quake was one of the largest ever recorded in Turkey. Survivors said it took two minutes for the shaking to stop.
The second earthquake - which was caused by the first - had a magnitude of 7.5, and its epicenter was in the Bostan district of Kahramanmaras province.
Many aftershocks are still being felt across the region.
The number of dead and wounded from both Turkey and Syria rose rapidly throughout Monday.
The World Health Organization has warned that those numbers are likely to increase by up to eightfold, as rescuers find more victims under the rubble.
"We always see the same thing with earthquakes, unfortunately, which is that initial reports of numbers of people dead or injured will increase exponentially in the week after that," WHO's chief emergency officer for Europe, Catherine Smallwood, told AFP.
Smallwood added that the snowy conditions will leave many people homeless, adding to the risks.
Many of the victims live in war-torn northern Syria, where millions of refugees live in camps on both sides of the border with Turkey. Dozens of deaths have been reported in rebel-held areas.
Thousands of buildings collapsed in both countries, and many videos show the moment they fell, as onlookers ran for cover. Many buildings that used to be as high as 12 stories are now flattened, roads are destroyed, and huge mountains of rubble lie as far as the eye can see.
Among the destroyed buildings was the Gaziantep Citadel, a historical landmark that has stood for more than 2,000 years.
The BBC's Middle East correspondent, Anna Foster, described in a report from the Turkish city of Osmaniye, near the epicenter, a devastating scene.
- “It is pouring rain, hampering rescue efforts. There is absolutely no electricity in the city tonight.