Hundreds are killed after one of the strongest earthquakes to hit Turkey in more than 100 years sent tremors across the region, collapsing buildings and sending residents running into the streets.

The 7.8-magnitude quake struck just after 4 a.m. Monday morning local time, 23 kilometers (14.2 miles) east of Nurdagi, Gaziantep province, at a depth of 24.1 kilometers (14.9 miles), the United States Geological Survey (USGS) said. Nurdagi is located along the Turkey-Syria border, and the quake was felt in several countries across the region, including Syria and Lebanon.

In Turkey, at least 1100 people were killed. In neighboring Syria, at least 830 people died, Syrian state news agency SANA reported, citing a Ministry of Health official. The deaths were reported in Aleppo, Latakia, Hama and Tartus.

Reuters put the number of injuries at thousands in the two neighboring countries.

Dozens of people are trapped under rubble, according to the “White Helmets” group, officially known as Syria Civil Defense, a humanitarian organization formed to rescue people injured in conflict. Much of northwestern Syria, which borders Turkey, is controlled by anti-government forces amid a bloody civil war that began in 2011.

The quake struck before daybreak on Monday, when residents were likely asleep and unprepared for the impact. Video from Turkey shared on social media showed dozens of collapsed buildings, while frightened residents huddled on the darkened streets amid the chaos. Rescue workers can be seen conducting search-and-rescue operations by flashlight.

Monday’s quake is believed to be the strongest to hit Turkey since 1939, when an earthquake of the same magnitude killed 30,000 people, according to the USGS. Earthquakes of this magnitude are rare, with fewer than five occurring each year on average, anywhere in the world. Seven quakes with magnitude 7.0 or greater have struck Turkey in the past 25 years – but Monday’s is the most powerful.

Karl Lang, an assistant professor at Georgia Tech University’s School of Earth and Atmospheric Sciences, told CNN the area hit by the quake Monday is prone to seismic activity. “It’s a very large fault zone, but this is a larger earthquake than they’ve experienced any time in recent memory,” Lang said.

Journalist Eyad Kourdi, who lives in Gaziantep and was staying with his parents when the earthquake struck early Monday, said “it felt like it would never be over.”

When the shaking stopped, Kourdi and his parents walked out of their home still wearing their pajamas, he said.

With several inches of snow on the ground, they waited outside in the rain for about 30 minutes before he could go back inside to grab coats and boots.

Strong aftershocks have been felt in southern and central Turkey. About 11 minutes after the main quake hit, the strongest aftershock of 6.7 magnitude hit about 32 kilometers (20 miles) northwest of the main quake’s epicenter. Another intense aftershock with a magnitude of 5.6 then occurred 19 minutes after the main quake.

Kourdi said there were up to eight “very strong” aftershocks in under a minute after the 7.8 magnitude quake struck, causing belongings in his home to fall to the ground. Many of his neighbors had left their homes following the quake, he said.

Photos showing the true scale of the disaster are emerging as day breaks in Turkey. Entire buildings have been flattened, with metal rods scattered across the streets. Cars have toppled over, while bulldozers work to clear the debris.

A winter storm in the region is exacerbating the disaster, according to CNN meteorologists.

“Hundreds of thousands of people are impacted by this. It is cold. It is rainy. Roads could be impacted, that means your food, your livelihood, the care for your children, the care for your family,” CNN meteorologist Karen Maginnis said.

“Anything as far as crops or anything growing across this region will be impacted as well. The ramifications of this are broad and will impact this region for weeks, and months.”

Searching for survivors

Search and rescue teams have been dispatched to the south of the country, Turkey’s interior minister, Suleyman Soylu, said. AFAD, the disaster agency, said it had requested international help through the Emergency Response Coordination Centre (ERCC), the European Union’s humanitarian program.

Nearly 1,000 search and rescue volunteers have been deployed from Turkey’s largest city, Istanbul, along with dogs, trucks and aid, according to its governor, Ali Yerlikaya.

“Sorry for our loss. I wish our injured a speedy recovery,” Yerlikaya wrote on Twitter.

The governor of Gaziantep, Davut Gul, said on Twitter that “the earthquake was felt strongly in our city,” and advised the public to wait outside their homes and stay calm.

“Please let’s wait outside without panic. Let’s not use our cars. Let’s not crowd the main roads. Let’s not keep the phones busy,” he said.

Gaziantep province has a number of small- and medium-sized cities, with a sizable refugee population, according to Brookings Institute fellow Asli Aydintasbas.

“Some of these areas are rather poor. Some are more richer, urban areas … but other parts that we’re talking about that seem to have been devastated, are relatively lower income areas,” she said.

Video from the city of Diyarbakir, to the northeast of Gaziantep, shows rescue workers frantically trying to pull survivors out of the rubble.

Turkish President Recep Tayyip Erdogan said the quake was felt in many parts of the country.

“I convey my best wishes to all our citizens who were affected by the earthquake that occurred in Kahramanmara? and was felt in many parts of our country. All our relevant units are on alert under the coordination of AFAD,” Erdogan wrote on Twitter.

Messages of condolences and support started pouring in Monday morning as world leaders woke to the news of the deadly earthquake.

White House National Security Adviser Jake Sullivan said the United States was “profoundly concerned” about the destruction in Syria and Turkey.

“I have been in touch with Turkish officials to relay that we stand ready to provide any & all needed assistance. We will continue to closely monitor the situation in coordination with Turkiye,” Sullivan wrote on Twitter.