Two Indian climbers have died on Mount Everest during a record-breaking period of ascents via Nepal's southern route, as experts warn of overcrowding on the world's highest peak.

"They fell ill while descending at high altitude. We are working out how to retrieve the bodies," Nivesh Karki, director at Pioneer Adventures, told AFP.

He named them as Sandeep Are, who he said summited on May 20, and Arun Kumar Tiwari, who reached the peak on May 21.

Nepal is home to eight of the world's 10 highest peaks and welcomes hundreds of adventurers each spring.

At least five climbers have died during this Everest season, including the two Indians and three Nepalis. A U.S. and a Czech climber died on Mount Makalu earlier this month.

Nepali climber Kami Rita Sherpa, who scaled Everest for a record 32nd time earlier this month, returned to the capital Kathmandu on Friday, where he expressed concern about the experience of some climbers.

Pictures posted by climbers show a long line of people climbing up fixed ropes, queueing in the icy, low-oxygen high-altitude zones.

"It was very crowded this year compared to last year because there was more clients," Kami Rita Sherpa told reporters at Kathmandu airport after flying back from the mountain. "There is a need for authorities to control this number."  

"They should let in only climbers of quality -- there should be a limit," he told AFP.

Records tumble 

On Thursday, a record number of climbers reached the 8,849-metre (29,032-foot) Himalayan peak from the Nepali side, according to tourism officials, who gave a preliminary total of 275 pending final confirmation.

The peak can be tackled from both Nepal and the northern face in Tibet, but Chinese authorities have closed the latter route this year.

The Guinness Book of World Records lists the highest number to climb Everest in a single day as 354, in May 2019.

Nepali tourism officials said the final number will be tallied after the climbs are verified, which require photographs and statements from the climber's expedition company and guides.

Among the successful climbers on Friday was British guide Kenton Cool, who reached the top for the 20th time — extending his own record for the most ascents of the world's highest peak by a non-Nepali.

The high number of climbers has rekindled concerns about overcrowding on the mountain -- especially if poor weather shortens the climbing window.

Approximately 600 people — including guides — have summited Everest since the start of this year's spring climbing season in April.

This year's Everest climbing season began late because of the risk from a huge serac hanging over the key route to the summit.

Mountaineering experts often criticize Nepal for letting many people try to scale Everest at the same time, which can produce risky congestion at some points. As a result, Nepal has imposed tighter controls and higher fees.

Thousands of people have climbed the peak since it was first scaled on May 29, 1953, by New Zealander Edmund Hillary and Sherpa guide Tenzing Norgay.