The death toll from this week's Himalayan flash floods has risen to 626 in Nepal and Tibet combined, authorities said, as Kathmandu appealed for foreign technical assistance while insisting it did not need help with general search and rescue. Nearly 2,500 people remain unaccounted for across the two countries, authorities said on Saturday. The number missing in Nepal had nearly doubled to 1,924, as more local residents were added to the list, while Tibet's toll stood at 554. More than 3,700 people have been rescued in Nepal so far, and hundreds of those missing are foreign nationals who had been working, trekking or travelling on pilgrimage in the region when the flood struck. Nepal's foreign minister, Shisir Khanal, told Reuters the government needed foreign expertise in specialised areas where it lacks the necessary skills, including rescuing people trapped in flooded tunnels, DNA testing, and storing bodies for longer periods as hospitals struggle to cope with the number of dead. "We have already made requests for such specialised services and technical assistance in areas where we don't have enough expertise and technical knowhow," he said. Britain, India, China, the United States, Britain, Japan, South Korea, Sri Lanka and Bangladesh have all asked to send their own search-and-rescue teams, according to the Kathmandu Post, but Mr Khanal said Nepali rescuers were already handling that work. "We think there is no need for repetition in this," he said.Rescuer load relief material in a helicopter to be transported to the areas affected by flash floods and a mudslide as it drizzles at the Maithali Barrack, an army training center, in Trishuli, Nuwakot district, Nepal (Reuters)A British rapid response team was due to arrive in Kathmandu on Saturday, tasked with assisting relatives of the more than 30 British nationals missing in the disaster. Forming part of the UK’s wider response to the flooding, which includes £5 million of humanitarian support for relief and recovery efforts, the team will also work with families in the UK concerned about loved ones in the affected area.Nepal has also asked India and China, the two larger neighbours between which it sits, to supply bailey bridges – portable, fast-assembly truss bridges that don’t need heavy machinery to install – to restore transport links after roughly two dozen bridges were destroyed in the flooding. Mr Khanal said many bodies had been recovered as far away as Chitwan and Nawalparasi, on the plains around 100 kilometres from the disaster zone, and that hospitals there had run out of refrigeration space to store them. He said the flood had caused extensive damage to schools, hospitals, hydropower plants, roads and bridges, and that Nepal would need further foreign support during reconstruction.Rescue operations entered a fourth day on Saturday, hampered by poor weather that grounded helicopters. Brig Gen Raja Ram Basnet, an army spokesperson, told the AP that rescue teams remained focused on the Upper Trishuli-1 hydropower project in Rasuwa district, where more than 100 people are believed trapped in a tunnel filled with thick mud. A person holds an umbrella as he stands in front of damaged buildings after flash floods and a mudslide, in Trishuli, Nuwakot district, Nepal (Reuters)Rescuers have used ropes and baskets to reach some of those trapped, he said, though the operation has been slowed by up to five feet of mud and a shortage of locations where helicopters can land. Teams have also had to relocate temporarily on at least one occasion after further flood warnings were issued.The renewed flood risk stems from a lake that formed high in the mountains after Wednesday's initial collapse and began overflowing this week. Monitoring data from China's ministry of water resources showed the lake's water level had dropped by 10 metres from its peak by late Friday, Chinese broadcaster CCTV reported, suggesting the immediate risk may be easing. Search teams also reached Gyirong Port, the border crossing on the Chinese side that was severely damaged in the flooding, with some rescuers reaching the area on foot, by raft, or via equipment lowered from drones.