Correction: An earlier version of this article incorrectly identified the scientific scale used to measure the magnitude of the quake and aftershocks. The U.S. Geological Survey uses the moment magnitude scale to describe earthquakes; it no longer uses the Richter scale. This version has been corrected.

Nepal’s capital became a city of whispers and rumors Sunday as residents hunkered down outdoors in tents and cars, and recurring aftershocks from Saturday’s earthquake kept everyone on edge, fearing another big quake.

Food and water supplies ran low. Price gouging began. Electricity was intermittent. Rescuers battled to make it to residents of remote villages — as well as climbers on Mount Everest — to save those still stranded more than 24 hours after the catastrophe. They continued clawing victims out of the rubble, sometimes with their bare hands.

The death toll kept climbing throughout the day and by early Monday it stood at more than 3,600 in Nepal and dozens more in neighboring countries.

On Sunday, Mass cremations began. Then it began to rain.

“I am stuck about [372 miles] northwest of Kathmandu in a village,” a despairing Ghanshayam Pandey, the director of a small charity, said in a telephone interview. “The deaths and injuries are overwhelming. We felt new tremors at 1 p.m. Nepal time. And it is raining off and on. It’s terrible.”

Sunday afternoon’s big aftershock in Nepal measured 6.7 on the moment magnitude scale, according to the U.S. Geological Survey, panicking already frightened citizens. As with the quake the day before, the aftershocks were felt as far away as New Delhi.

Two aircraft headed to Kathmandu’s Tribhuvan International Airport from India carrying some rescue personnel and aid workers had to head back to New Delhi because it was not safe to land, forcing a delay in relief efforts. Flights eventually resumed, only to be further delayed again by weather.

On Mount Everest, more snow and ice came crashing down, on the heels of Saturday’s devastating avalanche that left at least 19 reported dead at the mountain’s base camp and hampered rescues. Emergency personnel airlifted around 50 injured climbers by helicopter from the base camp Sunday morning but put help for others on hold after the aftershock. Col. Rohan Anand, a spokesman for the Indian army, said dozens of climbers remained missing at the world’s highest peak.

Among those killed on Everest were at least three Americans, according to the State Department: Dan Fredinburg, a Google executive from the San Francisco Bay Area; Marisa Eve Girawong, a physician’s assistant from Seattle; and Tom Taplin, a filmmaker from Colorado.

Outside Kathmandu, many rescue crews had yet to reach the more isolated villages, where authorities fear the devastation would be much worse. The Nepali military circulated aerial photos that showed entire villages flattened.

The United Nations issued a situation report that said that the most affected areas were Gorkha and Lamjung, areas northwest of Kathmandu and close to the quake’s epicenter, with damage to the Kathmandu Valley limited to historic, densely built-up areas. Hospitals were running out of room for storing corpses as well as emergency supplies, the report said.

A United Nations team arrived in Kathmandu on Sunday to assess the damage and identify the most urgent needs.

“It is essential that we move quickly and effectively,” said Jamie McGoldrick, the U.N. resident coordinator. “We need to ensure that no further lives are lost and the needs of the most vulnerable prioritized.”

The biggest challenge is that rescuers still don’t have reliable information about what’s going on in areas outside Kathmandu, including how many people are still trapped, according to O.P. Singh, the director general of India’s National Disaster Response Force.

“Where are they?” Singh said. “No assessment has been done.”

Relief agencies geared up for a humanitarian response to meet the massive shelter, food, clean-water and sanitation needs.

An urban search-and-rescue team from the Fairfax County Fire and Rescue Department in Virginia will be deployed, the U.S. Office of Foreign Disaster Assistance said on Twitter, with one from Los Angeles on standby.

The United States authorized an initial $1 million for emergency humanitarian needs, the State Department said.

By Sunday, international aid had begun to arrive. India deployed four military planes carrying tons of water and supplies, as well as ten National Disaster Response Force teams trained in search and rescue, and accompanied by sniffer dogs.

China, which gave $3 million in humanitarian aid, sent a ­62-member search-and-rescue team that arrived in Nepal on Sunday. More help is expected from Israel, Malaysia, Pakistan and Sri Lanka.

“The challenges are so many,” said Brad Kerner, an international public health specialist with Save the Children in Nepal. “The aftershocks and the scale of the tremors have created a lot of concern. There are a lot of people gathering outside in open spaces, and the markets and shops are closed. It’s going to be another night in tents or under the sky.”

Throughout Kathmandu on Sunday, even as rain began and darkness fell, people remained outside, too fearful of aftershocks to reenter their homes, gathering in parks, medians, school yards, anywhere there were open spaces.

Ram Bahadur Tandukar, 50, a public works contractor, was watching over his home from the street, where his extended family of five was sleeping crammed in a utility vehicle. During Sunday’s big aftershock, he said, he saw his house sway from left to right.

“There’s no way I want to go back,” he said. “The last two nights I have stayed in my car. It’s very cold, not comfortable. But I’m not getting out at all.”

At Bir Hospital — one of the oldest hospitals in Kathmandu — doctors had treated patients outside in the hours following the earthquake. They had treated more than 300 people and performed 38 back-to-back surgeries on their one functioning operating table, according to Kapil Gautam, a doctor there. Most of the patients had been hurt in roof and wall collapses. More than 100 bodies lay outside in the courtyard, including 10 that were uncovered and had yet to be identified.

Relatives of patients crammed the grounds outside, and the patients themselves sat on the floor in the foyer, too scared to stay in upstairs wards.

There, a truck driver named Dinesh Tamang comforted his wife, who had a swollen eye and a broken arm after the roof of the couple’s home collapsed Saturday. When the big aftershock occurred Sunday, Tamang said, his wife started screaming in fear.

“It was very scary for all of us, but I had to be strong,” he said. “I put my hand on her and said, ‘Don’t worry, the bad days will go soon.’­ ”

Prime Minister Sushil Koirala returned to Nepal on Sunday and immediately met with the cabinet of ministers. The government has directed all medical stores and large supermarkets to remain open. The cabinet also decided to conduct mass public funerals unless relatives claim victims’ bodies.

Saturday’s quake, which measured 7.8 on the Richter scale, had caused widespread damage throughout the Tibet region, India and Bangladesh. At least 62 people died in the Indian states of Uttar Pradesh, Bihar and West Bengal.

India’s prime minister, Narendra Modi, spoke of the devastation during his popular radio address Sunday.

“I can image what Nepal is going through, what the families of Nepal are going through,” Modi said. “We will try and save as many people as we can. We have to also concentrate on relief operation. The rehabilitation process will also take a long time.”

In the Tibet region of China, the death toll climbed to 20, with more than 200,000 affected. Houses and a historic temple collapsed. More than 1,500 officers from the People’s Liberation Army have been sent to the region to help in rescue operations, the government said.

Read more:

Experts had warned for decades that Nepal was vulnerable to a killer quake

Climbers trapped on Mount Everest ‘are getting desperate’

What Nepal’s earthquake felt like from a hotel in Kathmandu

Today's coverage from Post correspondents around the world

Gowen reported from Itanagar, India. Anup Kaphle in Washington, Simon Denyer in Beijing and Mrigakshi Shukla in New Delhi contributed to this report.