A second wave of deadly flash flooding could arrive in Nepal within days, authorities have warned as rescue teams faced a race against time to find survivors of a catastrophe that has already killed more than 350 people.A lake of rising water has formed along the Bhotekoshi river and the Nepalese disaster authorities fear it may yet burst its banks, urging residents and rescuers along the lower banks to move to safe areas.Nepalese monitors also warned that a section of the Trishuli River may have been blocked by debris during Wednesday’s floods, creating a landslide dam that could burst “imminently”.The fast-moving situation has complicated rescue efforts, with nearly 910 people still unaccounted for, including more than 500 foreigners and 33 British tourists swept up in the floods.A policeman with a sniffer dog looks at the damage in the aftermath of flash floods in Devighat in the Nuwakot district in Nepal, Thursday, Aug 27, 2026 (AP)The UK has offered £5 million to help Nepal during what the prime minister called a “very distressing and devastating situation”.Speaking to journalists during a visit to South Wales, Andy Burnham said: “It’s a devastating picture that is emerging from what has happened in Nepal.”“Obviously, there are a number of British nationals who currently are thought to be missing and we’ll be providing all the support we can to their families in what is a very distressing and devastating situation.”Two teenagers - a 13-year-old girl and a 14-year-old boy - are among the British nationals believed to be unaccounted for.Authorities were using helicopters to search for survivors and drop emergency supplies on Thursday after water and mud swept through Nepal’s Rasuwa, Nuwakot and Dhading districts.A Chinese national, who was airlifted from Rasuwa district, sits after he received first-aid at a mobile hospital inside the Maithali Barrack at Trishuli on Thursday (Reuters)The president of the Nepal Centre for Disaster Management, Dr Bishal Nath Upreti, said the situation on the ground was so dire that entire villages had been “wiped out”.“It was such a huge amount of water,” he said. “You can imagine it is 20 million cubic meters excess water on the river, and it was like a tsunami from the sky.”The National Disaster Risk Reduction and Management Authority in Nepal said that satellite information from China indicated that the Bhote Koshi river had been blocked, creating a risk of a second flood. In a post on social media, they said that information suggests "the lake is in the process of rising and there is a risk of bursting".Keshav Prasad Baral, a 68-year-old survivor being treated in a Nepali hospital, said: “It was a huge gush of mud coming straight towards us.”“As it got closer, it kept rising higher and higher. When I saw it enter our home, I tried to grab my wife's hand and take her to the terrace. But she was swept away by the mud.”Mud covering buildings and property following devastating floods at Trishuli, on Thursday (Reuters)A helicopter ferried him to safety four hours later. “My wife is still somewhere beneath the mud,” he told Reuters. “She's gone.”Rescue teams on the Nepali side said on Thursday that they had so far found 25 Chinese workers and around 100 Indian visitors, but 910 people were still missing.That figure included 517 foreign citizens, 44 soldiers and 28 police officers. Neighbouring India had the highest number of missing people with 178, the Nepali tourism industry said.The Red Cross said that entire villages had been destroyed and impassable roads and bridges had left communities cut off. The full scale of the disaster remains unclear, it added.Houses lying deluged in sludge after flash floods at Devighat (AFP/Getty)Unicef reported that least 17,000 children have been impacted by the floods. At least 14 children have been killed in the disaster, they said.“Children across Rasuwa and Dhading saw their lives being literally washed away in front of their eyes in a very short span of time, with homes, classrooms, and medical facilities damaged,” said Alice Akunga, UNICEF Representative to Nepal. “Too many lost their lives and loved ones. With the death toll still rising, we know this tragedy is far from over.”Meteorologists on the Chinese side warned of possible floods, landslides and other secondary disasters in the coming days, affecting Gyirong County.David Simon, professor of development geography at Royal Holloway, University of London, told The Independent that depressions that may seasonally fill up with water can create secondary disasters during periods of flooding. That could entail filling up and overtopping like dam overflows, or the force of the water rupturing part of the rim, he said.“What they will hopefully be doing is starting to monitor those sources very carefully ... and crucially starting to evacuate people and get as much of the infrastructure out of the way as possible. Given the remoteness, the topography, and so on, it's very unlikely that they'll be able to get large enough pumps to pump stuff out and prevent the catastrophe that way.”Dr Simon said the Himalayas had not seen flooding on such a scale before, and warned that it was only likely to continue as glaciers thin and summers continue to bring “extraordinary” weather.A girl cries while waiting for news of her late relatives after the floods in Bidur, in Nuwakot, Nepal, on 27 August (AP)Nepali officials have suggested an earthquake in the area could have caused the lower part of a glacier to collapse, triggering the catastrophic floods on Wednesday.Scientists have said that climate change is creating conditions that can destabilise high-mountain rock and ice, increasing the likelihood of disasters like this week’s flooding in the Himalayas.Benjamin Horton, dean of the School of Energy and Environment at the City University of Hong Kong, said Wednesday’s incident could be a classic example of a “compound event”.That happens when an earthquake interacts with climate-driven changes, such as glacier loss, thawing permafrost, and slope instability, to “create a more complex and damaging disaster than would occur from any one factor alone”, he told Reuters.