The World Health Organization has warned that the death toll from a strong earthquake in south-eastern Turkey, near Syria's border, could increase eightfold.
The death toll, which now stands at over 3,400, has risen rapidly since the first earthquake struck early Monday morning.
A second powerful tremor struck further north about 12 hours later.
To find survivors, rescuers have been combing through mountains of rubble in freezing and snowy conditions.
Turkey earthquake
OMAR HAJ KADOUR/AFP via Getty Images
Countries from all over the world are sending assistance, including specialist teams, sniffer dogs, and equipment, to aid in the rescue efforts, as per the BBC.
The 7.8 magnitude tremor struck at 04:17 local time (01:17 GMT) at a depth of 17.9km (11 miles) near the city of Gaziantep, according to the US Geological Survey.
The first quake, according to seismologists, was one of the largest ever recorded in Turkey.
According to survivors, the shaking lasted two minutes.
The magnitude of the second quake, which was triggered by the first, was 7.5, and its epicentre was in the Elbistan district of Kahramanmaras province.
Many aftershocks can still be felt throughout the region.
The number of people killed and injured in Turkey and Syria has risen rapidly throughout the day.
The WHO has warned that as more victims are discovered in the rubble, those numbers could rise by up to eightfold.
Many of the victims were killed in war-torn northern Syria, where millions of refugees are housed in camps on both sides of the Turkish border.
Several deaths have been reported in rebel-held areas.
Thousands of buildings have collapsed in both countries, and several videos showed the moment they fell as onlookers ran for cover.
Many 12-story-high buildings have been flattened, roads have been destroyed, and there are massive mountains of rubble as far as the eye can see.
Gaziantep Castle, a historic landmark that has stood for over 2,000 years, was among the buildings destroyed.
Anna Foster, the BBC's Middle East correspondent, described a devastating scene from the Turkish city of Osmaniye, near the epicentre.
Turkey's energy infrastructure has also been damaged, and videos of large fires in southern Turkey have surfaced.
Users on social media claimed they were caused by gas pipeline damage.
Fatih Donmez, Turkey's energy minister, confirmed serious infrastructure damage but did not mention the explosions.
Turkey is located in one of the most active earthquake zones on the planet.
A deadly earthquake in the northwest killed over 17,000 people in 1999. The worst earthquake disaster in the country occurred in 1939 when 33,000 people died in Turkey's eastern Erzincan province.
After a devastating earthquake ripped through Turkey and Syria, leaving destruction and debris on both sides of the border, rescuers are racing to pull survivors from beneath the rubble, as per CNN.
At around 4 a.m., one of the strongest earthquakes to hit the region in a century jolted resident awake on Monday, causing tremors in Lebanon and Israel.
According to Turkey's head of disaster services, Yunus Sezer, at least 2,921 people were killed and more than 15,800 were injured.
At least 1,451 people have died in neighboring Syria.
According to the Syrian state news agency SANA, 711 people have died in government-controlled areas, primarily in Aleppo, Hama, Latakia, and Tartus.
The "White Helmets" organization, officially known as the Syria Civil Defense, reported 740 deaths in opposition-held areas.
Anti-government forces control much of northwestern Syria, which borders Turkey, amid a bloody civil war that began in 2011.
Suleyman Soylu, Turkey's interior minister, said search and rescue teams had been dispatched to the country's south.
AFAD stated that it had requested international assistance through the European Union's humanitarian program, the Emergency Response Coordination Centre (ERCC).
According to the governor of Turkey's largest city, Istanbul, nearly 1,000 search and rescue volunteers have been deployed, along with dogs, trucks, and aid.
The World Health Organization's network of emergency medical teams in both countries has been activated to assist those affected by the earthquake, according to a tweet from the organization's director-general.
In his televised address, Erdogan also stated that NATO, the European Union, and dozens of other countries had offered assistance.
