More than 2,600 people have been reported killed and thousands more injured by a devastating earthquake 7.8 magnitude that struck south-eastern Turkey, near the Syrian border, in the early hours of Monday morning local time.
The death toll could rise eight-fold, the World Health Organisation has warned.
The US Geological Survey said the 7.8 magnitude tremor struck at 04:17 local time at a depth of 17.9km near the city of Gaziantep.
About 12 hours later, a second powerful tremor hit further north.
Seismologists said the first quake was the largest ever recorded in Turkey and survivors told BBC it took two minutes for the shaking to stop.
The second quake had a magnitude of 7.5 and an official from Turkey’s Disaster and Emergency Management Authority said it was independent of the earlier tremor and not an aftershock.
The death toll in Turkey has exceeded 1,650 while some 1,000 are confirmed to have died in Syria. Rescuers have been combing through mountains of rubble in freezing and snowy conditions to find survivors.
The WHO has warned that those numbers are likely to increase as much as eight times, as rescuers find more victims in the rubble.
We always see the same thing with earthquakes, unfortunately, which is that the initial reports of the numbers of people who have died or who have been injured will increase quite significantly in the week that follows,” said Catherine Smallwood of WHO.
Ms Smallwood added that the snowy conditions will leave many people without shelter, adding to the dangers.
Countries around the world are sending support to help the rescue efforts, including specialist teams, sniffer dogs and equipment.
At least 9,700 people have been reported injured in Turkey and 2,000 in Syria, however, those numbers have also been steadily rising.
Many of the victims are in war-torn northern Syria, where millions of refugees live in camps on both sides of the Syria-Turkey border. There have been dozens of fatalities reported in rebel-held areas.
Thousands of buildings have collapsed, and several videos show the moment they fell, as onlookers ran for cover. Many buildings that were four or five storeys high are now flattened, roads have been destroyed and there are huge mountains of rubble as far as the eye can see.
Among the buildings destroyed was Gaziantep Castle, an historic landmark that has stood for more than 2,000 years.
And a shopping mall in the city of Diyarbakir collapsed, a BBC Turkish correspondent there reported.
Turkey’s energy infrastructure has also been damaged, and videos posted by survivors show large fires in southern Turkey reported to have been caused by damage to gas pipelines.
Turkey’s Energy Minister confirmed there had been serious damage to the infrastructure.
Following an international appeal for help, Turkey’s President said 45 countries had offered support.
The European Union is sending search and rescue teams to Turkey, while rescuers from the Netherlands and Romania are already on their way. The UK has said it will send 76 specialists, equipment and rescue dogs.
France, Germany, Israel, and the US have also pledged to help. Russian President Vladimir Putin has offered help to both Turkey and Syria, as has Iran.
Turkey’s Interior Minister said 10 cities were affected by the initial quake and school has been suspended in those cities for at least a week.