Tens of thousands of Nepalese who spent the night under a chilly sky were jolted awake by strong aftershocks Sunday, while rescuers aided by international teams cleared rubble in search of survivors after a powerful earthquake killed nearly 2,000 people.

The number of casualties is expected to climb as reports come in from far-flung areas, said Home Ministry official Laxmi Dhakal. Among the dead are 17 who were struck by a quake-triggered avalanche on Mount Everest that buried part of the base camp packed with foreign climbers preparing to make their summit attempts.  At least 5,000 people were injured across Nepal.

Saturday's magnitude 7.8 earthquake, which was centered outside Kathmandu, the capital, was the worst to hit the poor South Asian nation in over 80 years. It destroyed swaths of the oldest neighborhoods of Kathmandu, and was strong enough to be felt all across parts of India, Bangladesh, China's region of Tibet and Pakistan. By Sunday morning, authorities said at least 1,970 people had died, all but 60 of them in Nepal. At least 721 of them died in Kathmandu alone.

"There were at least three big quakes at night and early morning. How can we feel safe? This is never-ending and everyone is scared and worried," said Kathmandu resident Sundar Sah. "I hardly got much sleep. I was waking up every few hours and glad that I was alive."

When the earth first shook, residents fled homes and buildings in panic. Walls tumbled, trees swayed, power lines came crashing down and large cracks opened up on streets and walls.

After the chaos of Saturday — when little organized rescue and relief was seen — there was more order on Sunday as rescue teams fanned out across the city. In the Kalanki neighborhood, police rescuers tried to extricate a man lying under a dead person, both of them buried beneath a pile of concrete slabs and iron beams. His family members stood nearby, crying and praying.

Police said the man's legs and hips were totally crushed.

"We are digging the debris around him, cutting through concrete and iron beams. We will be able to pull him out but his body under his waist is totally crushed. He is still alive and crying for help. We are going to save him," said police officer Suresh Rai.

Most areas were without power and water Sunday, but with Kathmandu airport reopened, the first aid flights began delivering aid supplies. Workers were sending out tents and relief goods in trucks and helicopters, said disaster management official Rameshwar Dangal.

He said government and private schools have been turned into shelters.

Roads to the Gorkha district, the quake's epicenter, were blocked by landslides, hindering rescue teams, said chief district official Prakash Subedi. Teams are trekking on foot through mountain trails to reach remote villages, and helicopters would also be deployed, he said by telephone.

Mukesh Kafle, the head of the Nepal Electricity Authority, said power has been restored fully to main government offices, the airport and hospitals.

But the damage to electricity cables and poles was making it difficult to restore power to many parts of the country, which has long been plagued by blackouts anyway.

"We have to make sure all cables are secure before turning the power on. Our technicians have been working round the clock," he said.

More than two dozen aftershocks jolted Nepal on Saturday and more hit on Sunday. Weather forecasts called for rain and thunder showers Sunday and the temperatures were in the mid-50s (about 14 Celsius), cold enough to make camping outside uncomfortable.

Still, thousands of people spent the night at Tudikhel, a vast open ground in the middle of Kathmandu, just next to the old city lined with historic buildings and narrow lanes. Now it is in ruins.

"We hardly slept through the night. It was cold and it rained briefly and it was uncomfortable, but I am glad I brought my family out to the open," said Ratna Singh, a vegetable vendor who was huddled under a blanket with his wife and son.

"At least I knew my family was safe. Every time the ground shook at night, I thanked God my family was there with me and safe. I don't think I am going to be sleeping inside the house anytime soon. We are all petrified," he said.

The quake will likely put a huge strain on the resources of this poor country best known for Everest, the highest mountain in the world. The economy of Nepal, a nation of 27.8 million people, relies heavily on tourism, principally trekking and Himalayan mountain climbing.

The world reacted quickly to the disaster, offering money, relief materials, equipment, expertise and rescue teams.

Among the first to move in was Nepal's giant neighbor India, with which it has close political, cultural and religious ties.

Indian air force planes landed Sunday with 43 tons of relief material, including tents and food, and nearly 200 rescuers, India's External Affairs Ministry spokesman Vikas Swarup said. The planes were returning to New Delhi with Indian nationals stranded in Kathmandu. More aid flights were planned for Sunday.

Hospitals in the Kathmandu Valley were overcrowded, running out of emergency supplies and space to store corpses, the United Nations said in a statement.

Officials said an avalanche after the quake swept the Everest base camp, flattening tents and killing at least 17 climbers and guides and injuring 61. Their nationalities were not immediately known. An unknown number were missing.

The U.S. Geological Survey put the magnitude of the quake at 7.8. It said the quake hit at 11:56 a.m. local time (0611 GMT) at Lamjung, about 80 kilometers (50 miles) northwest of Kathmandu. Its depth was only 11 kilometers (7 miles), the largest shallow quake since the 8.2 temblor off the coast of Chile on April 1, 2014.

The shallower the quake the more destructive power it carries.

The quake occurred at the boundary between two plates of Earth's crust, one of which holds India-Nepal and the other Eurasia to the north. The Indian plate is moving northward 45 millimeters (1.7 inches) a year under the Eurasian plate, said Marin Clark, a geophysicist at University of Michigan, Ann Arbor.

So the quake was "definitely not a surprise," she said. Over millions of years, such quakes have led to the uplift of the Himalayas. Nepal suffered its worst recorded earthquake in 1934, which measured 8.0 and all but destroyed the cities of Kathmandu, Bhaktapur and Patan.

While most modern buildings remained standing after the quake, it brought down several buildings in the center of the capital as well as centuries-old temples and towers.

Among them was the nine-story Dharahara Tower, a Kathmandu landmark built by Nepal's royal rulers as a watchtower in the 1800s and a UNESCO-recognized historical monument. It was reduced to rubble and there were reports of people trapped underneath.

The Kathmandu Valley is listed as a World Heritage site. The Buddhist stupas, public squares and Hindu temples are some of the most well-known sites in Kathmandu, and now some of the most deeply mourned.

The head of the U.N. cultural agency, Irina Bokova, said in a statement that UNESCO was ready to help Nepal rebuild from "extensive damage, including to historic monuments and buildings of the Kathmandu Valley."

Nepali journalist and author Shiwani Neupane tweeted: "The sadness is sinking in. We have lost our temples, our history, the places we grew up."

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Naqvi reported from New Delhi. Associated Press writers Ashok Sharma and Tim Sullivan in New Delhi and Seth Borenstein in Washington, D.C. contributed to this report.