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Nepal earthquake: Major aftershock hits Kathmandu as toll climbs

The aftershock sparked screams and sent terrified people into the streets of Kathmandu.

KATHMANDU, Nepal — A major aftershock hit the Kathmandu area of Nepal on Sunday, terrifying residents as rescuers dug for survivors of a devastating earthquake that left more than 3,200 people dead.

The U.S. Geological Survey said the tremor registered an initial 6.7 magnitude — compared with Saturday's 7.8-magnitude quake.

The aftershock sparked screams and sent terrified people into the streets of Kathmandu. At the city's airport, the floor rolled with the tremor. Passengers rushed past the immigration desks and customs officials abandoned their seats, rushing to take cover along a row of pillars as the building shook and lights briefly went out.

On Mount Everest — where an avalanche triggered by Saturday's quake killed at least 18 people — climbers reported further avalanches.

Related: Nearly 1,900 dead after massive earthquake devastates Nepal

More than 3,200 people were known dead as of Monday morning, according to Nepal's Interior Ministry and national police.

At least three U.S. citizens were confirmed dead, according to a State Department official, who declined to comment further "out of respect for the privacy of those affected."

After thousands of people slept in the open air in Nepal, rescuers dug with their bare hands Sunday to continue searching for survivors and bodies. Police Officer Sudan Shreshtha said his team had taken 166 corpses overnight to one hospital in Kathmandu.

"I am tired and exhausted, but I have to work and have the strength," Shreshtha told Reuters as an ambulance brought three more victims to the Tribhuvan University Teaching Hospital.

Thousands of people were gathered near the Tudikhel Parade Ground, some with tents, while others lay on blankets in the large grassy area.

"I've never seen this situation in my life," said Subhas, who had spent the night there. "It's totally horrible."

Subhas, 30, told NBC News he did not know whether his rental home was still standing.

Soro, a 15-year-old student, was also staying at the parade ground with his family and described how his family's apartment shook "horizontally and vertically" when the quake hit. He said that two of his aunts were hospitalized with scrapes but that the rest of his family was uninjured.

"Yesterday was a catastrophe," Subhas said.

As aid started flowing into Nepal, Save the Children said on Twitter that its teams on the ground "found the overall situation to have been worse than their worst fears."

Several nations have pledged to send help. The U.S. pledged an initial $1 million in humanitarian aid, and on Sunday it deployed a military C-17 Globemaster aircraft carrying 70 personnel, including a response team, a search-and-rescue team and journalists. The plane, which was also carrying 45 square tons of cargo, was expected to arrive in Nepal on Monday, said Col. Steve Warren, a Pentagon spokesman.

The European Union said it is ready to support an international aid effort, and Pakistan said it would send doctors, hospital equipment and search-and-rescue teams. China was sending a 62-member search-and-rescue team and six dogs, which were expected to arrive Sunday afternoon, state-run media Xinhua reported.

Indian air force planes landed Sunday with 43 tons of relief material, including tents and food, along with nearly 200 rescuers, according to Vikas Swarup, a spokesman for India's External Affairs Ministry. India's prime minister said a high-level meeting would be held to discuss further aid efforts.

Rescue helicopters also managed to make it to Mount Everest to airlift some of the badly wounded off the peak. Officials confirmed that 17 bodies had been recovered there — and that more than 60 people were injured in the avalanche on what is believed to have been the deadliest day ever recorded on the world's tallest mountain.

— Vinograd reported from London. NBC News' Wajahat S. Khan in Islamabad, Phil Helsel in Los Angeles, The Associated Press and Reuters contributed to this report.

This story originally appeared on NBC News