An 85-year-old ex-Gurkha who was attempting to reclaim his title as the world's oldest person to summit Mount Everest died of altitude sickness, the expedition organiser said Sunday.

Min Bahadur Sherchan died at Everest base camp on Saturday and his body was airlifted to Kathmandu.

"Doctors said that he died of natural causes. There was water build-up in his lungs because of altitude sickness," Shiv Raj Thapa of Summit Nepal Trekking told AFP after an autopsy.

Sherchan was resting at the base camp and waiting for the weather window to summit in a single attempt, skipping the usual multiple acclimatisation rotations because of his age.

He was on a bid to reclaim a title that he lost to Japanese mountaineer Yuichiro Miura in 2013.

The former soldier became the oldest person to summit Everest in 2008 when he was 76, but he lost the record five years later when Miura reached the 8,848-metre peak at the age of 80.

Speaking to AFP earlier this year, the slightly hard of hearing grandfather said he just wanted to prove to himself that he could still make it to the top of the world.

"My aim is not to break anybody's record, this is not a personal competition between individuals. I wish to break my own record," Sherchan had said in February.

Sherchan's death is the second fatality of the spring climbing season on Everest, which runs from late April to the end of May.

Experienced Swiss climber Ueli Steck died last month when he fell from a steep ridge during an acclimatisation exercise.

Nearly 750 people will this year attempt to summit the world's highest mountain during the narrow window of good weather that usually falls in mid-May.

Hundreds of climbers have been on Everest for weeks to acclimatise before making a bid for the top.

This year is particularly crowded as it is the last chance for climbers who were forced off the mountain by the devastating 2015 earthquake to use their extended permits. This has raised concerns about dangerous traffic jams on the mountain.

Mountaineering is a major revenue earner for impoverished Nepal, home to eight of the world's 14 peaks over 8,000 metres