Mountaineers and authorities at Everest base camp in Nepal have told the BBC they are seeing rising numbers of climbers with Covid-19 symptoms and rising numbers of positive tests, raising fears of a serious outbreak.
Base camp officials said they had received reports of 17 confirmed cases from hospitals in the capital Kathmandu, where a number of climbers have been sent from the base camp and higher camps to be treated.
And staff at a private hospital in Kathmandu, the CIWEC clinic, confirmed to the BBC that patients had tested positive for coronavirus after arriving from Everest base camp.
The Nepalese government has so far denied having any knowledge of positive cases at Everest base camp, raising concerns that officials are downplaying the extent of the situation out of fear it will bring more pressure to close the mountain to expeditions.
Foreign climbers are a major source of revenue for the Nepalese government, which shut Everest last year during the pandemic.
Authorities are mandating that visiting climbers quarantine in Nepal before proceeding to base camp, but concerns have been raised within the climbing community that a serious outbreak at the mountain would be devastating.
The number of coronavirus cases has risen sharply in Nepal in recent weeks, and the country has the highest rate of infection among the countries neighbouring India, where a second wave has sparked a full-blown crisis.
Officials from Nepal's Department of Tourism, which directly oversees expeditions, could not be reached for comment, but Prem Subedi, the under-secretary at Nepal's Ministry of Culture, Tourism and Civil Aviation, told the BBC the ministry was not aware of any coronavirus cases at base camp.
"None of the Covid cases at Everest base camp have been reported so far to the Ministry of Tourism," he said.
The Himalayan Rescue Association, which runs a government-authorised medical clinic at the base camp, told the BBC it had received confirmation of positive cases in some climbers flown out to Kathmandu by expedition teams.
"We have just received from Kathmandu confirmation of 17 positive cases [in climbers flown out of Everest]," said Lhakpa Nuru Sherpa, an official with the Himalayan Rescue Association.
"We have now asked expedition teams to first let us know before they fly out their members [to Kathmandu] who fall ill so that we know what is going on," he said.
Lhakpa Nuru Sherpa's colleague at the Everest base camp clinic, Dr Prakash Kharel, said the number of people showing coronavirus-like symptoms, such as a persistent cough and fever, was rising daily
"Almost all climbers get a cough here, but we are seeing people with other symptoms, and we are making sure that they stay in isolation," Dr Kharel said.
The CIWEC clinic in Kathmandu also confirmed to the BBC that it had seen Covid-positive climbers come to them as patients from Everest.
"We did have patients come to us from the Everest region who tested positive at our hospital a couple of weeks back," said staff member Astha Pant. "We cannot share how many people or any other information at this time."
One of the big expedition teams, who asked not to be named, told the BBC that some of their members had previously tested positive, but had now recovered. A Norwegian climber, Erlend Ness, told the BBC that he had tested positive for the virus three times in two different hospitals in Kathmandu last month.
Ness was initially thought to be suffering from altitude sickness, but was diagnosed with coronavirus after being airlifted from base camp. Climbers have raised fears that coronavirus symptoms would be mistaken for the similar effects of being at altitude.
"You can hear people coughing everywhere," Lukas Furtenbach, team leader of Furtenbach Adventures, told the BBC from base camp. "But this is not just the regular cough that mountaineers catch here. You can make it out that people are in pain and they have other symptoms like fever and body aches."
According to the website of the Department of Tourism, the government had issued 394 Everest climbing permits for this climbing season, as of 26 April. That would allow more than 1,500 people to be on the mountain, the majority of them support staff.
Officials at Everest base camp said there was also concern over climbers coming back from Kathmandu either after Covid treatment or after acclimatisation rotation to adjust to the altitude.
"They may have recovered themselves but they might bring the virus along with them as things are getting serious in Kathmandu," said the army official. "We have therefore recommended that climbers do the rotation acclimatisation at places below the base camp, instead of going to Kathmandu."
No Covid testing facility
Mountaineers and officials at the Everest base camp also said that the lack of a coronavirus testing facility at the base camp health clinic was a major handicap.
"We had requested a testing facility but the government said they could not give the permission," said Dr Kharel.
Some of the big expedition teams have said they have brought their own testing kits to Everest base camp, which has helped them to take timely steps like isolating people and evacuating them.
Himalayan Rescue Association officials said they had only recently received the confirmed reports of 17 positive coronavirus cases in climbers from Everest base camp.
"It is unfortunate that we have not been receiving the details of the confirmed cases and the identities of the climbers all this time," an army official at the base camp told the BBC.
"That would have helped us in contact tracing and containing the spread much earlier," he said. "We could have then isolated the climbers who had come in contact with those who tested positive much earlier."