A Norwegian climber has become the first to test positive for Covid-19 at Mount Everest base camp.
Erlend Ness was flown by helicopter to Kathmandu, where he was admitted to hospital.
He told the Associated Press that he tested positive on April 15.
Mr Ness said another test on Thursday was negative and he is now staying with a local family in Nepal.
Any outbreak could prematurely end the climbing season, just ahead of a window of good weather in May, the Austrian said.
“We would need now most urgently mass testing in base camp, with everyone tested and every team being isolated, no contact between teams,” said Mr Furtenbach.
“That needs to be done now, otherwise it is too late.”
Mr Furtenbach, leading a team of 18 climbers to Mount Everest and its sister peak Mount Lhotse, said there could be more than just one case on the mountain as the Norwegian had lived with several others for weeks.
Mira Acharya, director at the Department of Mountaineering, said she had no official information about the Covid-19 cases and only reports of illnesses such as pneumonia and altitude sickness.
Mountaineering was closed last year due to the pandemic and climbers returned to Everest this year for the first time since May 2019.
The popular spring climbing season in Nepal, which has eight of the highest peaks in the world, began in March and ends in May.