At least 12 Nepalese climbing guides have been killed after an avalanche struck Mount Everest early today.

It is believed to be the worst accident to hit the world's highest peak.

The climbers had been preparing the route to the summit ahead of the main climbing season, which kicks off later this month.

The death toll is expected to rise, Lakpa Sherpa from the non-profit Himalayan Rescue Association said at Everest base camp.

The avalanche occurred at around 6.45am (2am Irish time) at an altitude of about 5,800 metres in an area known as the "popcorn field".

The area lies on the route into the treacherous Khumbu icefall, Ang Tshering Sherpa, president of the Nepal Mountaineering Association, said.

A young Nepalese guide who survived the accident has recalled being "trapped" after the avalanche came crashing down.

Dawa Tashi Sherpa, 22, was rescued after being buried neck-deep in the snow.

The force of the avalanche fractured his ribs and broke his shoulder blades, but he is expected to make a full recovery.

"I don't know how I survived," he said, after being airlifted to Kathmandu's Grande International Hospital.

He was among a large party of Sherpas carrying tents, food and ropes who headed out for an early morning expedition.

Sherpa Dawa said he left the base camp at around 3am local time, armed with equipment to help fix ropes for commercial climbers.

As he scaled the mountain slopes in the dark, climbing ladders and walking on ice, dozens of guides kept him company, with several ahead of him and others behind.

The avalanche struck soon after daybreak. "It came out of nowhere, this huge block of ice that fell from above, flying right at us," Sherpa Dawa said.

"I wanted to run but there was no time, we were just trapped."

Despite being hit by the full force of the avalanche, he said he managed to breathe and was conscious, though suffering from hypothermia.

He was eventually found by rescuers and airlifted to Kathmandu.