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, said.

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

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 US 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.