A huge queue of climbers formed near the summit of Mount Everest on Thursday. (File)

Three more climbers have died on Everest, expedition organisers and officials said Friday, taking the toll from a deadly week on the overcrowded peak of the world's tallest mountain to seven.

Nepal has issued a record 381 permits costing $11,000 each for this year's spring climbing season, triggering bottlenecks en route to the summit after poor weather cut down the number of climbing days.

"Two more Indian climbers have died on Everest yesterday," Mira Acharya, spokeswoman for Nepal's Tourism Department, told AFP, while expedition organisers confirmed the third fatality.

Kalpana Das, 52, reached the summit but died on Thursday afternoon while descending, as a huge number of climbers queued near the top of Mount Everest.

Another Indian climber, 27-year-old Nihal Bagwan, also died on his way back from the summit.

"He was stuck in the traffic for more than 12 hours and was exhausted. Sherpa guides carried him down to Camp 4 but he breathed his last there," said Keshav Paudel of Peak Promotion.

An Austrian climber died on the northern Tibet side of the mountain, his expedition organiser said.

The 65-year-old died close to the summit on his descent.

Wednesday saw an Indian, 55-year-old Anjali Kulkarni, and American climber die on the mountain. Last week, an Indian climber died and an Irish mountaineer is presumed dead after he slipped and fell close to the summit.

Ang Tsering Sherpa, former president of the Nepal Mountaineering Association, said that the weather window to summit this season was narrow, meaning that many teams were still waiting to go up.

"Spending a long time above the death zone increases the risk of frostbite, altitude sickness and even death," he said.

Big Business

Mountaineering in Nepal has become a lucrative business since Edmund Hillary and Tenzing Norgay made the first ascent of Everest in 1953.

The Himalayan nation has issued a record 381 permits costing $11,000 each for this year's spring climbing season, triggering bottlenecks en route to the summit after poor weather cut down the number of climbing days.

Most Everest hopefuls are escorted by a Nepali guide, meaning more than 750 climbers were expected to tread the same path to the top in the current season.

At least 140 others have been granted permits to scale Everest from the northern flank in Tibet, according to expedition operators. This could take the total past last year's record of 807 people reaching the summit.

Many Himalayan mountains -- including Everest -- are at peak climbing season, with the window of good weather between late April and the end of May.

At seven other climbers have died on other 8,000-metre Himalayan peaks this season, while two are missing.

In 2015, 18 people were killed at the base camp because of an avalanche triggered by a quake.