The dramatic floods sent water and mud surging through the communities of Timure, Timure, Rasuwagadhi and others along the Trishuli river corridor, according to Intrepid, sweeping away homes, bridges and roads. The flooding also affected the Bhote Koshi river.

Police in Nepal on Thursday (27 August) said the death toll had risen to 270 with more than 800 people missing. In neighbouring Tibet, which was also hit by the torrents, more than 550 are understood to be missing, although national and international media outlets warn there could be some overlap in the figures.

The flooding along the Bhote Koshi and Trishuli rivers hit the communities of Rasuwa, Nuwakot, Dhading and Gorkha at around 8.30am local time on Wednesday, according to the Nepal Tourism Board.

It said a "preliminary, agency-wide" record from trekking and travel companies operating in the affected region had identified some 644 travellers reported missing, including 33 UK nationals and two from Ireland.

The tourism board said government, civil and police agencies, as well as tourism stakeholders, were continuing to work towards verifying the whereabouts and safety status of those tourists and travellers who were in the region, liaising with travel agencies, guides, local authorities and security agencies.

Twelve of the 33 missing UK nationals were travelling with Alpine Eco Trek, according to an earlier update from the tourism board. It has so far identified 10 tourism agencies known to have had travellers in the region at the time.

One of the 10, Nepalese tour operator The Trekkers' Society, has confirmed to the PA news agency nine British citizens were completing one of its tours when the floods came. Its general manager said it had not been able to make contact with the tour guide.

'Support critical'

Intrepid, which runs 26 itineraries in Nepal and had 76 local team members there, has confirmed no Intrepid travellers or team members were in the affected regions at the time, and that all Intrepid travellers in the country are accounted for.

It has partnered with the Australian Red Cross, which is providing emergency relief in Nepal, for the appeal, which is being administered by the not-for-profit Intrepid Foundation. The operator will match all funds raised up to the first £50,000.

"The disaster has caused widespread damage to homes, businesses, roads and critical infrastructure, with communities facing a long and challenging recovery," said Intrepid. "All funds raised will go towards impacted communities, including emergency shelter support, water sanitation and hygiene, first aid and health services."

Yalamber Rai, Intrepid's General Manager in Nepal, said: "The scale of this disaster is devastating. Communities across the region are grieving the loss of loved ones while also facing significant challenges in the weeks and months ahead.

"Support will be critical to recovery efforts, and we are encouraging anyone who is able to donate to the appeal or help spread the word. Together, we can help ensure affected communities receive the support they need during this incredibly difficult time."

'Changing situation'

The Foreign Office had updated its travel advice for Nepal in light of the emergency, warning flooding in Nepal's Rasuwa district and along the Nepal-China border has caused "widespread damage".

"Buildings, roads, other transport and communications infrastructure have been severely damaged," reads the updated FCDO advice. "Other areas in Nepal, including Chitwan, have also been affected." It is warning the situation "may change rapidly".

"If you are travelling in the region, follow the advice of the Nepalese government and local authorities and be alert to the changing situation. The Nepalese government has established a toll-free emergency Nepalese language number, 1234, and a dedicated hotline 1144 accessible in Nepal."