At nightfall, Nepal’s capital became a tent city, as thousands of residents displaced by Saturday’s devastating earthquake stayed in their dark gardens and out on the cracked streets and lanes, afraid to go back inside because of waves of aftershocks, including a powerful jolt Sunday that the U.S. Geological Survey said measured 6.7 magnitude and which sent people fleeing for open ground and safety.

It had been a pleasant Saturday morning, with families just sitting down to lunch and tourists thronging to Kathmandu’s Durbar Square when the temblor hit, a horrible rocking motion that seemed to go on without end. The quake was ultimately felt across South Asia — in Lahore, in New Delhi, in Dhaka. Snow avalanched down Mount Everest. Buildings fell, mud-joined huts collapsed. By the end of the night, more than 1,900 lay dead, Nepalese officials said, with countless more injured.

And another kind of death: Durbar Square — the historic heart of Kathmandu, filled with temples centuries old — lay in ruins. More than 100 people were killed at that site alone. The iconic Dharahara tower fell, too. “There’s nothing left,” one despairing survivor told CNN-IBN, an Indian news channel.

“We never imagined that we would face such devastation,” Nepal’s information minister, Minendra Rijal, said at an evening news conference — even though Kathmandu ranks high on a list of the world’s cities most likely to experience a devastating earthquake. He said schools would be closed for five days in affected areas. He encouraged people to conserve fuel by not driving and urged pharmacies to stay open all night so that the injured could have ­access to first-aid supplies and medicine.

In Washington, Secretary of State John F. Kerry said the United States had authorized an initial $1 million for emergency humanitarian needs. USAID is preparing to send a disaster response team and is likely to also send a specialized urban search-and-rescue team, the State Department said.

“To the people in Nepal and the region affected by this tragedy we send our heartfelt sympathies,” Kerry said. “The United States stands with you during this difficult time.”

National Security Council spokeswoman Bernadette Meehan also expressed condolences and said the United States “stands ready to assist the government and people of Nepal and the ­region further.”

The Israeli army said in a statement Saturday that it would send military airplanes filled with equipment and personnel to assist in rescue efforts in Nepal, including medical, search-and-rescue and logistical professionals.

Israeli Foreign Minister Avigdor Lieberman told state TV that efforts would also include sending incubators to help transfer to safety about 24 babies born in the past few days to surrogate mothers in Nepal for Israeli parents. Some were born prematurely, and hospitals in areas hit by the quake could no longer care for them, Israeli news media reported.

Countries such as Sri Lanka and Pakistan also moved to help. India dispatched planes and rescue personnel with three tons of supplies and a mobile hospital, and 15 helicopters were to arrive Sunday. Nepal appealed to China for aid.

As Nepalese emergency personnel and volunteers worked to pull bodies from the rubble, hospitals and rescue crews were quickly overwhelmed. Patients from neighboring areas flooded Kathmandu’s medical facilities, and traffic clogged damaged roads, hindering relief efforts.

At Kathmandu Medical College and Teaching Hospital, staff were doing what they could to triage patients, said Patrick Adams, a freelance multimedia journalist who described the scene. Many were still covered in soot. Broken limbs were quickly splinted with cardboard. The worst cases were taken directly to surgery. The 11-bed intensive-care unit could not handle the influx. The dead were lined up on the pavement outside; many had been crushed.

“One woman was shrieking over her dead husband, climbing over him, pulling his face to hers, refusing to be led away,” Adams recounted.

Shops around Kathmandu ran low on bottled water, food and phone cards. Eventually, many closed. Mosques and youth centers opened shelters, and the government set up tents and began distributing food.

Families huddled together as night fell. A chill passed over the devastated city, and rain was on the way. People worried about aftershocks. There had ­been dozens.

“We’re very afraid,” said Lhakpa Sherpa, a Mount Everest guide staying outside his home in the capital with his wife and daughter. “We can still feel the shakes.”

In the Tahachal neighborhood, a 66-year-old cellphone distributor named Laxmi Narayan was camped outside with his wife, two sons, a brother, sister-in-law and two nephews. He was still reeling from the shock on what had been such an ordinary day, from the chaos that descended as he sat at his desk on his half-day at work.

It was an ordeal just trying to reach his family afterward, he said. “The roads were cracking before us.”

Now he was wondering what the coming hours would bring.

“We have no food, no water or electricity. There is no TV or radio service that can keep us updated on what is happening. We are too scared to go back into our homes,” Laxmi said. “The army is trying to rescue people, but the government is helpless. The government is not at all equipped to handle a calamity of this magnitude. We need help from people who have experience to handle this kind of situation.”

It seemed as if Saturday’s temblor was the earthquake everybody in Nepal had long feared — the big one. The last time such a terrible quake occurred was in 1934, when an estimated 8,000 people were killed. But the country’s disaster preparedness was so uneven and its earthquake likelihood so dire that the U.N. Office for Disaster Risk Reduction issued a report in 2012 that called Nepal “a tragedy in waiting.”

The U.S. Geological Survey said the quake hit at 11:56 a.m. in Lamjung and was considered a “shallow quake,” which can be worse than deeper temblors. It was the largest shallow quake since the 8.2 temblor off the coast of Chile on April 1, 2014.

Outside Kathmandu, many rescue crews had yet to reach the more isolated villages. Nepalese Finance Minister Ram Sharan ­Mahat said on Twitter that a night-vision helicopter had been ­deployed to Barpak in Gorkha district, thought to be near the epicenter. The reported number of dead in Gorkha had reached 47.

On Mount Everest, several climbers were believed to have died and others were missing after the earthquake triggered a massive avalanche, authorities said.

One of the climbers who died was Google executive Dan Fredinburg, the head of privacy for Google X. Fredinburg had been enthusiastically posting about his mountain-climbing adventure on Instagram and Twitter, and his sister confirmed his death on ­social media Saturday.

The earthquake also caused loss of life and damage in other countries. At least 34 people died in India, and casualties were reported in Tibet and Bangladesh. India’s foreign secretary, S. Jaishankar, said in a news conference that a building at the Indian Embassy complex in Nepal collapsed and the daughter of an employee had been killed.

As rescue operations continued through the night, relief agencies geared up for a humanitarian response to meet shelter, food, clean water and sanitation needs.

“The situation is quite bad, and the cold weather is not going to help,” said Tony Castleman, the country head of Catholic Relief Services in New Delhi, where workers were planning to ship blankets and other supplies. “It’s going to be tough to sleep in the open.”

According to Nepal’s Information and Communications Ministry, the government has decided to open immigration services at all hours and provide free visas to members of foreign aid organizations who want to come to Nepal for rescue and relief efforts. The government has approved about $5 million for immediate use.

One key area of need is medical care and supplies.

Chakra Raj Pandey, the head of Grande International Hospital, one of the largest private hospitals, said the facility was running short on emergency drugs such as adrenaline and oxygen and other medications needed for patients in intensive care. The hospital’s large grounds are crowded with scared, hungry and crying patients.

“The influx is so huge, it’s difficult to cope with the pressure,” Pandey said. “The government is not really prepared. We are getting no help or guidance from them. We are shocked. We don’t know what the days ahead will be like. The first day, few hours, we are suffering so much. What will ­happen later?”

Lakshmi reported from New Delhi and Kaphle from Washington. Mrigakshi Shukla in New Delhi, Anne Gearan in Washington and Ruth Eglash in Jerusalem contributed to this report.