KATHMANDU, Nepal » Planeloads of supplies, doctors and relief workers from neighboring countries began arriving Sunday in Nepal, a poor Himalayan nation reeling from a powerful earthquake that killed more than 1,900 people and destroyed infrastructure, homes and historical buildings.

The disaster’s international reach was also apparent on the slopes of Mount Everest where an avalanche triggered by Saturday’s earthquake left at least 17 people dead and 61 injured.

The magnitude-7.8 earthquake, which was centered outside Kathmandu, the capital, was the worst to hit the South Asian nation in more than 80 years. It destroyed swaths of the oldest neighborhoods of Kathmandu, and was strong enough to be felt across parts of India, Bangladesh, 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 died in Kathmandu alone, and the number of injured nationwide was upward of 5,000.

Tens of thousands of Nepalese who spent the night under a chilly sky were jolted awake by strong aftershocks Sunday.

"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."

As day broke, rescuers aided by international teams set out to dig through the rubble of buildings — concrete slabs, bricks, iron beams, wood — to look for survivors. Most areas were without power and water. The United Nations said hospitals in the Kathmandu Valley were overcrowded, and running out of emergency supplies and space to store corpses.

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 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.

The quake will likely put a huge strain on the resources of this impoverished 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.

With the Kathmandu airport reopened, the first aid flights began delivering supplies. The first to respond were Nepal’s neighbors — India, China and Pakistan, all of which have been jockeying for influence in the landlocked nation. Still, Nepal remains closest to India with which it shares deep 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.

The United States is sending a disaster response team and $1 million in aid to Nepal. The White House and Secretary of State John Kerry offered condolences along with pledging the support.

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

After the chaos of Saturday — when little organized rescue and relief was seen — there was more order Sunday as rescue teams fanned out across Kathmandu.

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.

Mukesh Kafle, 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.

The U.S. Geological Survey said the quake’s epicenter was Lamjung, about 50 miles northwest of Kathmandu, in Gorkha district. Its depth was only 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.

Roads to the Gorkha district 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.

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 1.7 inches a year under the Eurasian plate, said Marin Clark, a geophysicist at the University of Michigan at 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.

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.

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