KATHMANDU (REUTERS) - Thousands of desperate Nepalese spent a second night in the open in the early hours of Monday, unable to return to homes either flattened by Saturday's devastating earthquake or at risk of collapsing in a series of powerful aftershocks.

Across the capital, Kathmandu, and beyond, exhausted families lay mattresses out on streets and erected tents to shelter from rain. The sick and wounded also lay out in the open, unable to find beds in the city's overwhelmed hospitals.

Outside Kathmandu Medical College, surgeons set up an operating theatre inside a tent.

People queued for water dispensed from the back of trucks, while the few stores still open had next to nothing on their shelves. Crowds jostled at one pharmacy to snap up medicine.

High in the Himalayas, hundreds of foreign and Nepalese climbers remained trapped after a huge avalanche killed 17 people in the worst single disaster to hit Mount Everest.

Nearly 2,500 people were confirmed killed in the 7.9 magnitude quake, making it the worst such disaster to hit Nepal since 1934 when 8,500 died. Thousands more were injured.

The death toll is likely to climb as rescue workers struggle to reach remote regions in the impoverished, mountainous country of 28 million people and as bodies still buried under rubble are recovered.

With so many people sleeping in the open with no power or water and downpours forecast, fears mounted of major food and water shortages. Across the country, hundreds of villages have been left to fend for themselves. "We are overwhelmed with rescue and assistance requests from all across the country," said Deepak Panda, a member of the country's disaster management.

Several countries rushed to send aid and personnel.

India flew in medical supplies and members of its National Disaster Response Force. China sent a 60-strong emergency team. Pakistan's army said it was sending four C-130 aircraft with a 30-bed hospital, search and rescue teams and relief supplies.

A Pentagon spokesman said a U.S. military aircraft with 70 personnel left the United States on Sunday and was due in Kathmandu on Monday.

Britain, which believes several hundred of its nationals are in Nepal, said it was delivering supplies, medics and search and rescue teams.

But there has been little sign of international assistance on the ground so far, with some aid flights prevented from landing by aftershocks that closed Kathmandu's main airport several times on Sunday.

The disaster has underlined the woeful state of Nepal's medical facilities. The country has only 2.1 physicians and 50 hospital beds for every 10,000 people, according to a 2011 World Health Organization report.

"The earthquake has exposed that Nepal's best public hospital infrastructure has crumbled at a time when it should serve more people in a hurry," said Sarvendra Moongla, a senior surgeon at Bir Hospital's Trauma Centre in Kathmandu, which opened in February.

At the Tribhuvan University Teaching Hospital, bodies, including that of a boy aged about seven, were heaped in a dark room. The stench of death was overpowering.

Outside, a 30-year-old woman who had been widowed wailed: "Oh Lord, why did you take him alone? Take me along with him."

Rajiv Biswas, Asia Pacific chief economist at business research firm IHS, said long-term reconstruction costs in Nepal using proper building standards for an earthquake zone could be more than $5 billion, or around 20 percent of the country's GDP.

"With housing construction standards in Nepal being extremely low ... the impact of the earthquake has been devastating based on initial reports," he said in an early analysis of the likely damage.

In crowded Kathmandu, many buildings were flattened or badly damaged.

Nepali army officer Santosh Nepal and a group of rescuers worked all night on Saturday to open a passage into a collapsed building in Kathmandu. They used pick axes because bulldozers could not get through the ancient city's narrow streets. "We believe there are still people trapped inside," he told Reuters, pointing at concrete debris and twisted reinforcement rods where a three-storey residential building once stood.

Among the capital's landmarks destroyed in the earthquake was the 60-metre Dharahara Tower, built in 1832 for the queen of Nepal.