A powerful 7.8 magnitude earthquake rocked wide swaths of Turkey and Syria early Monday, toppling hundreds of buildings and killing more than 2,300 people. Hundreds were still believed to be trapped under rubble, and the toll was expected to rise as rescue workers searched mounds of wreckage in cities and towns across the area.

On both sides of the border, residents jolted out of sleep by the pre-dawn quake rushed outside on a cold, rainy and snowy night. Buildings were reduced to piles of pancaked floors, and major aftershocks continued to rattle the region.

Rescue workers and residents in multiple cities searched for survivors, working through tangles of metal and concrete. A hospital in Turkey collapsed, and patients, including newborns, were evacuated from facilities in Syria.

In the Turkish city of Adana, one resident said three buildings near his home were toppled. “I don’t have the strength anymore,” one survivor could be heard calling out from beneath the rubble as rescue workers tried to reach him, said the resident, journalism student Muhammet Fatih Yavus.

“Because the debris removal efforts are continuing in many buildings in the earthquake zone, we do not know how high the number of dead and injured will rise,” Turkish President Recep Tayyip Erdogan said. “Hopefully, we will leave these disastrous days behind us in unity and solidarity as a country and a nation.”

The quake, which was centered north of the Turkish provincial capital of Gaziantep, was felt as far away as Cairo. It sent residents of Damascus rushing into the street, and jolted awake people in their beds in Beirut.

It struck a region that has been shaped on both sides of the border by more than a decade of civil war in Syria. On the Syrian side, the swath affected is divided between government-held territory and the country’s last opposition-held enclave, which is surrounded by Russian-backed government forces. Turkey, meanwhile, is home to millions of refugees from that conflict.

The opposition-held regions in Syria are packed with some 4 million people displaced from other parts of the country by the fighting. Many of them live in buildings that are already wrecked from past bombardments. Hundreds of families remained trapped in rubble, the opposition emergency organization, called the White Helmets, said in a statement.

Strained health facilities and hospitals were quickly filled with wounded, rescue workers said. Others had to be emptied, including a maternity hospital, according to the SAMS medical organization.

The region sits on top of major fault lines and is frequently shaken by earthquakes. Some 18,000 were killed in a similarly powerful earthquakes that hit northwest Turkey in 1999.

The U.S. Geological Survey measured Monday’s quake at 7.8. Hours later, a 7.5 magnitude one struck more than 100 kilometers (60 miles) away. An official from Turkey’s disaster management agency said it was a new earthquake, not an aftershock, though its effects were not immediately clear. Hundreds of aftershocks were expected after the two temblors, Orhan Tatar told reporters.

Thousands of buildings were reported collapsed in a wide area extending from Syria’s cities of Aleppo and Hama to Turkey’s Diyarbakir, more than 330 kilometers (200 miles) to the northeast. A hospital collapsed in the Mediterranean coastal city of Iskenderun, but casualties were not immediately known, his vice president, Fuat Oktay, said.

Televisions stations in Turkey aired screens split into four or five, showing live coverage from rescue efforts in the worst-hit provinces. In the city of Kahramanmaras, rescuers pulled two children alive from the rubble, and one could be seen lying on a stretcher on the snowy ground.

Offers of help — from search-and-rescue teams to medical supplies and money — poured in from dozens of countries, as well as the European Union and NATO.

The damage evident from photos of the affected areas is typically associated with a significant loss of life — while bitterly cold temperatures and the difficulty of working in areas beset by civil war will only complicate rescue efforts, said Dr. Steven Godby, an expert in natural hazards at Nottingham Trent University.

In Turkey, people trying to leave the quake-stricken regions caused traffic jams, hampering efforts of emergency teams trying to reach the affected areas. Authorities urged residents not to take to the roads. Mosques around the region were opened to provide shelter for people unable to return to damaged homes amid temperatures that hovered around freezing.

The quake heavily damaged Gaziantep’s most famed landmark, its historic castle perched atop a hill in the center of the city. Parts of the fortresses’ walls and watch towers were leveled and other parts heavily damaged, images from the city showed.

In Diyarbakir, hundreds of rescue workers and civilians formed lines across a mountain of wreckage, passing down broken concrete pieces, household belongings and other debris as they searched for trapped survivors while excavators dug through the rubble below.

In northwest Syria, the quake added new woes to the opposition-held enclave centered on the province of Idlib, which has been under siege for years, with frequent Russian and government airstrikes. The territory depends on a flow of aid from nearby Turkey for everything from food to medical supplies.

The opposition’s Syrian Civil Defense described the situation there as “disastrous.”

Osama Abdelhamid, who was being treated for injuries at a hospital in Idlib, said most of his neighbors died. He said their shared four-story building collapsed just as he, his wife and three children ran toward the exit. A wooden door fell on them and acted as a shield.

“I was reborn, thank God,” he said.

In the small Syrian rebel-held town of Azmarin in the mountains by the Turkish border, the bodies of several dead children, wrapped in blankets, were brought to a hospital.

The Directorate-General of Antiquities and Museums in Syira said the earthquake has caused some damage to the Crusader-built Marqab, or Watchtower Castle, on a hill overlooking the Mediterranean. Part of a tower and parts of some walls collapsed.

The USGS said the quake was centered about 33 kilometers (20 miles) from Gaziantep. It was 18 kilometers (11 miles) deep.

More than 1,000 people were killed in 10 Turkish provinces, with some 7,000 injured, according to the country’s disaster management agency. The death toll in government-held areas of Syria climbed over 370 people, with some 1,000 injured. In rebel-held areas, more than 200 people were killed, according to the White Helmets, though the SAMS medical organization put the toll at more than 135; both said hundreds were hurt.

Huseyin Yayman, a legislator from Turkey’s Hatay province, said several of his family members were stuck under the rubble of their collapsed homes.

“There are so many other people who are also trapped,” he told HaberTurk television by telephone. “There are so many buildings that have been damaged. People are on the streets. It’s raining, it’s winter.”