Thirty-three British citizens including a 13-year-old girl are among more than 400 travellers missing after a flash flood on the Nepal-Tibet border, according to Nepal’s tourism board.

The sudden flood happened on the Tibetan side of the Bhote Koshi River at about 8.30am local time on Wednesday. The 33 UK citizens are among at least 341 foreign nationals unaccounted for.

Earlier on Wednesday, the tour operator Alpine Eco Trek said a 13-year-old girl was among the missing British nationals, as well as two Irish citizens.

Among the missing British nationals are three men aged 65, 64, and 52, and seven women aged 44, 47, 51, 60, 63, 63, and 65, according to travel logs.

The firm, which offers guided tours and expeditions in Nepal, confirmed four of its Nepali tour guides – aged 38, 35, 45 and 29 – are missing as well.

Kumar Adhikari, the manager of Alpine Eco Trek, said on Wednesday: “I feel so sad. We are just thinking about what to do next.

“We are in pain at the moment, deep pain.”

Adhikari said the tour group, who were on a nine-day tour to Mount Kailash, were crossing into Tibet from Nepal when they became trapped at the border as the flash floods struck.

He said he was in contact with his tour guides until 8.40am when their phones went offline, at which point the group would have been inside Tibet’s immigration office.

“We were hoping that inside it was safe,” he said. “But later the video came from China’s government which (showed) even Tibet’s side was hit by the flood.”

The tourist board said more than 100 of the missing people were yet to have a nationality confirmed.

Police in Nepal said 157 bodies had been recovered and more than 40 people were injured and receiving treatment in hospital.

A wall of mud and rock appeared to have collapsed into the river on the Himalayan border of Nepal and Tibet, triggering catastrophic flooding on the Nepali side, Reuters reported. It said verified ​videos showed dozens of people being swept away at the border.

Houses, roads and energy infrastructure were destroyed in Nepal, while officials in Tibet said they feared “major casualties”, with some people missing in the county of Gyirong after ⁠a mudslide hit a border land crossing.

Initial reports suggested an earthquake had triggered an avalanche and caused the floods, Shisir Khanal, Nepal’s foreign minister, told the country’s parliament.

Eight South Koreans working on a hydropower plant ⁠were missing ⁠and ​10 others stranded, South Korea’s foreign ministry ⁠said.

Local authorities said tourists in the Rasuwa district of Nepal and other areas along the Bhote Koshi and Trishuli rivers should “exercise extreme caution”, remain in safe areas and move to higher ground if required.

Visitors were urged to stay in regular contact with hotels and travel agencies. People planning to travel to the affected areas in the coming days were warned to postpone their journeys.

The UK’s foreign secretary, Ed Miliband, said: “I am deeply concerned to hear of the flash floods on the Nepal-China border. All my thoughts are with those affected and with British nationals in the area and their relatives here at home.”

The British embassy in Kathmandu urged people in affected areas to follow local advice. A joint statement with the embassies of Australia, the EU, Finland, France, Norway and Switzerland said: “We are deeply saddened by the devastating flooding in Rasuwa and Nuwakot districts and surrounding areas. Our thoughts are with all those affected by this disaster. We express our solidarity with the people of Nepal during this difficult time.

“We encourage all those in affected areas to follow the guidance of local authorities and official safety advisories as the situation continues to evolve.”