Death toll on traffic-jammed Mount Everest hits 11

Dozens of climbers line up to stand at the summit of Mount Everest.

A US climber has died after descending from Everest, officials said Tuesday, taking this season's toll to 11 including several deaths blamed on overcrowding on the world's highest mountain.

American Christopher John Kulish, 61, had already climbed the 8,848-metre (29,029-feet) peak, and was safely back at a camp below the summit on Monday evening.

"All of a sudden he had a heart problem and passed away at South Col, according to his expedition organisers," said Mira Acharya from Nepal's tourism department.

An Australian climber meanwhile was recovering in hospital in Kathmandu, officials said, after reportedly being found lying unconscious above 7,000 metres (23,000 feet).

The reports said that Gilian Lee from Canberra was attempting to climb the northern flank of Everest from Tibet without supplementary oxygen.

Nepal issued a record 381 Everest permits this season and a short weather window resulted in some teams waiting several hours in the dangerous "dead zone", running out of oxygen supplies and risking exhaustion.

At least four of the deaths this season -- the deadliest since 2015 when massive earthquakes triggered avalanches that swept away climbers' camps -- have been blamed on the delays.

As well as the Everest deaths, nine climbers have died on other 8,000-metre Himalayan peaks, while one person is missing.

In addition to the Nepal permits that cost $11,000 each, at least 140 others were granted permission to climb from the northern flank of Everest in Tibet.

Although final numbers are yet to be released with the season ending this week, together with the accompanying sherpa guides this could take the total past last year's record of 807 people reaching the summit.