Evert-Jan Daniels / ANP / AFP - A dutch rescue team departs from Eindhoven Airport in the Netherlands 

With fears rising of food and water shortages, Nepalis were rushing to stores and petrol stations to stock up on essential supplies in the capital Kathmandu, left devastated by Saturday's 7.8-magnitude quake.

Officials say more than 4,100 people are now known to have died, including 4,010 in Nepal -- making it the quake-prone Himalayan nation's deadliest disaster in more than 80 years.

More than 90 people have been killed in neighbouring India and China while a further 7,500 people were injured in Nepal.

But senior disaster management official Rameshwor Dangal said the toll in Nepal could jump once rescuers discovered the full extent of devastation in villages.

"Rescue operations are underway, and in many places where buildings have collapsed there might be people trapped," Dangal, the home ministry's national disaster management chief, told AFP.

"We are also in the process of getting information from villages, and these will add to the death toll."

Families who work in Kathmandu were packing onto buses, some even sitting on the roofs, leaving the city, many for their home villages to determine the damage there.

Mothers clutching children and men hauling bags were seen bargaining with drivers of the many buses clogging the roads out of the capital.

The exodus came as international rescue teams with sniffer dogs raced to find survivors , and teams equipped with heavy cutting gear and relief supplies landed at the nation's only international airport.

Hospitals have been overwhelmed, with morgues overflowing and medics working flat out to cope with an endless stream of victims suffering trauma or multiple fractures.

Nearly a million children living in affected areas are in urgent need of humanitarian assistance, UNICEF said.

Elisabeth Byrs, a spokeswoman for the UN's World Food Programme, told AFP the agency would launch a "large, massive operation" with the first plane carrying rations set to arrive on Tuesday.

Reconstruction efforts in impoverished Nepal could cost more than $5 billion, or around 20 percent of the country's GDP, according to Rajiv Biswas, Asia Pacific chief economist at business research firm IHS.

Pledging $10 million in relief to help the victims, US Secretary of State John Kerry said he had been shocked by the "gut-wrenching" images of the death and destruction.

British officials said a military transport plane laden with supplies and dozens of Nepalese Gurkha soldiers serving in the British army would take off from a UK air base headed for their homeland.

Fear of diseases

Across Kathmandu, Nepalis were hunkered down for the night in makeshift tents in parks and other open spaces, many having lost their houses and others too terrified to return home after several powerful aftershocks.

"This is a nightmare. Why don't these aftershocks stop?" asked 70-year-old Sanu Ranjitkar, clutching her dog and with an oxygen mask strapped to her face as she sat under a tarpaulin.

With just plastic sheets to protect them from the elements, many were desperate for aid and information on what to do next.

"There is just too much fear and confusion," said Bijay Sreshtha, who fled to a park with his three children, wife and mother when the quake hit.

Fears were rising of a disease outbreak in the multitude of tent camps that have sprung up around the city.

"Right now, it is important to prevent another disaster by taking precautions against an outbreak of diseases among the survivors," army official Arun Neupane told reporters.

Long queues formed outside petrol stations while supermarkets were seeing a run on staples such as rice and cooking oil.

A government official said tonnes of clean water and other essential supplies were needed for survivors as well as stepped-up search and rescue efforts outside the capital.

"We need more helicopters for our rescue operations in rural areas," home ministry spokesman Laxmi Prasad Dhakal told AFP.

"We also need supplies of essential goods such as food and clean water to provide relief for survivors."

Areas affected include , the world’s highest mountain, where the quake triggered an avalanche that killed at least 18 people.

Rescue helicopters on Monday airlifted climbers from higher altitudes on the mountain where they were stranded above crevasses and icefalls, after evacuating scores of seriously injured from base camp the day before.

Hundreds of mountaineers had gathered at Everest at the start of the annual climbing season, and the real scale of the disaster there has been impossible to evaluate with communications all but cut off.