A huge, unstable chunk of glacier is blocking the route up Mount Everest from Base Camp in Nepal just as peak climbing season gets under way in the Himalayas.
"Icefall doctors" – who fix ropes and ladders on the lower part of the route up the world's highest peak - can find no way round the 100-foot-high (30m) block of ice just under Camp 1.
They say the only option is to wait for the ice block, called a serac, to melt – which they hope will happen within days.
The delay means preparations are weeks behind schedule for the spring season when weather for Everest ascents is usually best, and fears are growing that climbers will be queuing to reach the summit again this year.
Purnima Shrestha, a prominent climber and photographer from Nepal, is currently acclimatising to summit Everest for the sixth time.
"We usually climb between Camp I, Camp 2 and Camp 3 back and forth during this acclimatising process. Delays in the opening of the route have added concerns of possible 'traffic jams' to the peak this year," she told the BBC from Base Camp.
The icefall doctors work for the Sagarmatha Pollution Control Committee (SPCC) that is responsible for securing ropes as far as Camp 2 on Everest, which stands 8,848.86m (29,031 feet) above sea level. They reached Base Camp three weeks ago.
By this stage in April they would normally have fixed the route as far as Camp 3, but are still blocked by the chunk of glacier about 600m below Camp 1.
"We haven't found artificial ways to melt it so far, so we don't have any options other than to wait for it melting and crumbling itself," SPCC base camp co-ordinator Tshering Tenzing Sherpa told the BBC.
Ang Sarki Sherpa, who has worked as an icefall doctor for years, said he expected the serac to melt because its lower part was weak.
"We reached it on 10 April. The crevasse below is melting," he said, adding that Sherpas after him said it had melted further and was close to collapsing.
He and other climbers have not seen a way of safely bypassing the serac and say a possible alternative route to Camp 1 would be challenging to put up this year. Scaling the huge serac has been deemed too risky.
"There is no choice. We spent four days touring the area, looking at every place from the mountain to the right and left," Ang Sarki Sherpa said over the phone from Base Camp.
Nepal's Department of Tourism says it's exploring different options, including airlifting teams to Camp 2.
"We are thinking about airlifting the rope-fixing team and their logistics to Camp 2 by helicopter, so they can open the route above that altitude for now," Ram Krishna Lamichhane, the department's director general, said.
"We will wait for the ice to melt at the place where there is an obstruction and work there when everything is safe."
Favourable weather is expected only until the end of May, and with the melting of the ice currently obstructing the route, Sherpas hope the rope-fixing work to Camp 2 will be completed within a few days - and the summit within a week.
But Purnima Shrestha said that even if the route is opened soon, the climbing window could be reduced this season. She summitted Everest three times in a single season in 2024, having made the first push for the summit on 11 May that year.
"I am not worried that the route won't open because we still have time for that. But the window could be narrow – with lots of climbers having to make their attempts in a short period of time."
Despite the Iran war - and its impact on fuel costs and travel – large numbers of people are expected to attempt Everest this year.
"There has been a slight decrease due to the impact of flights, but mountaineering has not been affected as much as trekking," said Dambar Parajuli, president of the Expedition Operators' Association.
According to the Department of Tourism, 367 people have so far obtained climbing permits, most of them Chinese. According to climbing organisers, China has not issued permits for foreign nationals from its territory this year.
Most Everest ascents are from Nepal rather than via the easier route from Tibet. Last year, more than 700 people, including guides, summited from the Nepalese side, while only about 100 people climbed from China.
Since photos of climbers queuing on Mount Everest went viral in 2019, Nepal has been tightening its permit system and sharply increasing prices.
Climbing fees for Everest in spring have been hiked this year to $15,000 (£11,105) from $11,000 for foreign nationals. For Nepalis it's doubled to $1,000.
