A magnitude-6.1 earthquake hit Afghanistan early on Wednesday, killing at least 920 people, Reuters reported citing disaster management officials.
More than 600 people injured and the tolls are expected to grow as information trickles in from remote mountain villages.
Photographs published by Afghan media showed houses reduced to rubble, with bodies swathed in blankets lying on the ground.
Helicopters were deployed in the rescue effort to reach the injured and fly in medical supplies and food, said an interior ministry official, Salahuddin Ayubi.
"The death toll is likely to rise as some of the villages are in remote areas in the mountains and it will take some time to collect details."
Wednesday's quake was the deadliest since 2002. It struck about 44 kilometers from the southeastern city of Khost, near the border with Pakistan, the U.S. Geological Survey (USGC) said.
Most of the confirmed deaths were in the eastern province of Paktika, where 255 people were killed and more than 200 injured, Ayubi added. In the province of Khost, 25 were dead and 90 had been taken to hospital.
Haibatullah Akhundzada, the supreme leader of the ruling Taliban, offered his condolences in a statement.
Mounting a rescue operation could prove a major test for the Taliban, who took over the country in August and have been cut off from much international assistance because of sanctions.
Shaking was felt by about 119 million people in Pakistan, Afghanistan and India, the European-Mediterranean Seismological Centre (EMSC) said on Twitter, but there were no immediate reports of damage or casualties in Pakistan.
The EMSC put the earthquake's magnitude at 6.1, though the USGC said it was 5.9.
Adding to the challenge for Afghan authorities is recent flooding in many regions, which the disaster agency said had killed 11, injured 50 and blocked stretches of highway.
The UN's office for the Coordination of Humanitarian Affairs (UNOCHA) said Afghanistan had asked humanitarian agencies to help with rescue efforts, and teams were being dispatched to the quake-hit area.
A spokesman of Afghanistan's foreign ministry said it would welcome international help. Neighboring Pakistan said it was working to extend assistance.
Afghanistan is frequently hit by earthquakes, especially in the Hindu Kush mountain range, which lies near the junction of the Eurasian and Indian tectonic plates.
Scores of people were killed and injured in January when two quakes struck rural areas in the western province of Badghis, damaging hundreds of buildings.
In 2015, more than 380 people were killed in Pakistan and Afghanistan when a magnitude-7.5 earthquake ripped across the two countries, with the bulk of the deaths in Pakistan.