LONDON — International aid agencies and governments mobilized on Sunday to respond to the earthquake in Nepal, saying they faced challenges in getting assistance to the country and distributing it amid the widespread devastation there.

In the aftermath of the disaster, which has killed more than 3,200 people, injured about 5,900 and left many more homeless, development workers said that continued aftershocks, a crippled transportation network and the loss of power in parts of the country had made it tough to search for survivors and distribute much-needed supplies. More stories after the cut...

Employees of aid groups have been affected themselves as they organize responses to the catastrophe. Sanjay Karki, the country director for Mercy Corps, an international aid organization, said that some members of his staff had lost their homes, and that although his own house was still standing, his extended family in Katmandu was camping outside until the aftershocks subsided.

The United States, India and China initiated relief efforts that were expected to send substantial numbers of foreign aid workers, search-and-rescue teams and medical equipment to the stricken country over the next couple of days.

“We’re just gearing up,” said Roger Hodgson, deputy country director in Nepal for Save the Children, an international charity that already has more than 400 people, mostly Nepali, in the country. “People have been resilient. But it’s been difficult to get people and supplies into the country, especially to rural areas far from Katmandu.”

The United Nations has said that more than six million people live in the areas of Nepal that have been affected. Many individuals have either lost their homes or have been forced to live on the streets because of the threat of further aftershocks. The global response is being coordinated by the Nepalese government through its National Emergency Operation Center.

“What’s important to remember about Katmandu is that it’s densely, densely packed,” said Gary Shaye, the director of humanitarian operations for Save the Children who worked in Nepal in the 1970s and 1980s. “This is a village that grew into a city.” He added, “There is not a lot of open space to accommodate people who get displaced.”

Rain descended on Katmandu on Sunday, and Mr. Shaye said that the relief efforts faced a “race against time” because the monsoon season begins in June.

“Even if we had all the plastic sheeting and temporary shelter, is this going to be adequate for the monsoon season?” he asked.

Still, because a severe earthquake has long been predicted by geologists, some agencies had made preparations and disaster plans. “There was a sense of readiness you always have to have,” said Sarah Crowe, the crisis communications chief of Unicef, who has also worked in Nepal. She said Unicef had supplies of tents, plastic sheeting and buckets, as well as zinc and oral hydration solutions for children who might be dehydrated from diarrhea. “It won’t be enough, and more shipments will have to be brought in.”

“This was a tragedy waiting to happen,” she added, noting that under an earthquake preparation program, whistles had been given to some schoolchildren in case they got covered in rubble.

Experts said, however, that remote areas, some of which are reachable only on foot, may have to wait longer to receive help. Nepal’s poor road network, a limited number of helicopters and planes to shuttle supplies to distant villages, and intermittent communications throughout the country would likely worsen the current situation, they said.

“People can’t get blankets, cooking equipment and other supplies in rural villages,” said Mr. Hodgson of Save the Children. “The problem is getting that type of kit on the ground.”

While Katmandu’s airport remains open, disaster-relief experts already in Nepal said that less than a fifth of the regular daily flights were now arriving, as airlines were concerned about the effect of aftershocks.

“Toward evening, hospitals were trying to accommodate a huge influx of patients, some with amputated limbs, and were running short of supplies like bandages and trauma kits,” Jamie McGoldrick, the United Nations resident coordinator in Nepal, said in a statement on Sunday.

“Water supplies, a problem under normal circumstances in this fast-growing city, will almost certainly run short,” he added. “Search-and-rescue personnel will face the challenge of reaching villages nearer the quake’s epicenter.”

A United States disaster relief response team of almost 70 people is expected to arrive on Monday, according to Susan Parker-Burns, a spokeswoman for the United States Embassy in Katmandu. Two teams of American Special Forces were already in Nepal on a training exercise, and were providing logistical and medical support to the country’s army, she added.

Several of Nepal’s neighbors have sent help. India said that it had sent 13 military transport planes and a 40-person disaster response team, and China said that a search-and-rescue team had already reached Katmandu.

The Israeli military said it was preparing to send two Boeing 747s carrying 260 aid workers and more than 90 tons of cargo to Katmandu on Monday.

Several European governments have also offered financial resources and personnel. On Sunday, the British government said it had made $7.5 million available to charities already working in Nepal so that they could buy essential supplies. Norway has pledged $4 million, and other European countries, like Germany, France and Spain, said they would offer financial support.

As the death toll from the earthquake continued to rise, however, aid agencies said that more support would be needed, particularly as attention turns beyond the initial response to the long-term support needed to rebuild many parts of Nepal.

As people affected by the earthquake tried to contact friends and families, several technology companies also offered their support, but their services still depended on Nepal’s patchy Internet and cellphone coverage.

Google said that it had activated its Person Finder tool that allows individuals to post information about their condition or to try to find missing family members. The service had previously been used after the earthquake in Haiti in 2010 and the tsunami that struck Japan in 2011.

Facebook said that it had turned on a tool for people in Nepal to let their friends and family know that they are O.K.