Inside Nepal's race against time as dozens of British nationals remain missing

Good evening . It all began at 8:37 a.m. local time last Wednesday . A chunk of ice broke off from a glacier near the border between China and Nepal . Half an hour later and the water levels in the Trishuli River had risen by 9 m . Then the river burst its banks and this happened . A torrent of ice, rock, mud, and debris swept away homes, roads, bridges, and power plants . More than a thousand people were killed and thousands more are unaccounted for . The result of climate change, according to Nepal's Prime Minister . Scientists agree, but also point to a lack of disaster preparedness in the region . It needs sirens . It needs an understanding of how people understand hazard . It needs to be conveyed in a language that they understand . There is definitely a lot of potential to avoid such a huge loss of life as we have seen in the last couple of days . Rescuers are now trying to reach hundreds of workers who sought refuge in tunnels . Hydroelectricity accounts for 90% of Nepal's electricity supply and there are several power plants dotted along the main riverbank . More than 270 people have been rescued from hydropower projects so far . Coming up, we'll focus on the unique challenges facing search and recovery teams . Let's get started with tonight's first report from John Sparks from northern Nepal . In a town called Trishuli, they've turned the playing field into an airfield where the choppers come and go . Some ferry emergency supplies upriver . Some bring survivors to town . And the names of people who've been rescued are then added to this list . But Karma can't find her brother's name . He lived in a riverside town called Betrawati . It's difficult, isn't it? It 's a difficult time . Oh, it's been difficult . I'm struggling to take it all in, she told me . With 4,000 people still missing in Nepal , the rescue effort depends on helicopters like these , commandeered from local tour operators . We're on day seven of this disaster