KATHMANDU: At least 12 Nepalese guides preparing routes up Mount Everest for commercial climbers were killed on Friday by an avalanche in the deadliest mountaineering accident ever on the world’s highest peak, officials said.

The men were among a large party of Sherpas who left Everest base camp before dawn, carrying tents, food and ropes, in an early morning expedition ahead of the main climbing season starting later this month.

Four were still missing, tourism officials said, while one rescuer at the scene said he expected the death toll to rise by at least three after other bodies were spotted.

The avalanche occurred at around 6:45am at an altitude of about 5,800 metres (19,000 feet) -- in an area nicknamed the “popcorn field” due to ice boulders on the route leading into the treacherous Khumbu icefall.

“We have retrieved 12 bodies from the snow,” Nepal tourism ministry official Dipendra Paudel said in Kathmandu.

Deteriorating weather conditions forced rescuers to suspend searches for the missing until Saturday morning, Paudel said. “We do not want to risk another accident,” he said.

Aided by rescue helicopters, at least seven people were plucked alive from the mountain and the injured were sent to hospital in the capital.

One survivor said dozens of guides were on the move when the avalanche hit.

“It came out of nowhere, this huge block of ice that fell from above, flying right at us,” Dawa Tashi Sherpa said from his hospital bed in Kathmandu.

“I wanted to run but there was no time, we were just trapped,” the 22-year-old guide said.

The force of the avalanche fractured Sherpa’s ribs, broke his shoulder blades and left him buried in neck-deep snow, before rescuers found him and had him airlifted to the capital.

Kathmandu-based expert Elizabeth Hawley, considered the world’s leading authority on Himalayan climbing, said the avalanche was the most deadly single accident in the history of mountaineering on the peak.

The previous worst accident on Everest occurred in 1996 when eight people were killed during a storm while attempting to summit the mountain, first conquered in 1953 by Sir Edmund Hillary and Tenzing Norgay.