Hundreds of tourists, including 12 Britons and three Americans, are missing after devastating flash floods and mudslides wiped out buildings and bridges along the Nepal-Tibet border. 

Houses and roads were swept away in Nepal by rushing water and mudslides while officials in China-controlled Tibet said they feared 'major casualties' with some missing in the county of ​Gyirong after a mudslide hit a land crossing between the neighbours this morning. 

At least 95 people have been confirmed dead following the natural disaster, amid fears that many more will be found as search and rescue operations get underway. 

Terrifying footage shows a tsunami wave of flood water crashing through a town, sweeping away everything in its path in the mountainous Rasuwa region of Nepal. 

In Tibet, one clip showed the Gyirong Port land crossing being annihilated by the flood. Dozens of people were seen running away in terror seconds before the water and mud crashed into the structure and wiped it out. 

Experts believe a 4.4-magnitude quake triggered an ice avalanche which in turn blocked the Lhende river. Water then built up behind the blockage before bursting downstream with devastating consequences. 

There are fears that a second flood may send Nepal, Tibet and neighbouring India into further chaos. Flood alerts were issued in the populous northern Indian states of Uttar Pradesh and Bihar as they border Nepal and several rivers flow down the mountains into their plains. 

Among the unaccounted are 12 from the UK - including a 13-year-old girl -  105 Indian nationals, four from South Africa, 17 from Malaysia and three from the United States. One each from Australia and the Netherlands are also unaccounted for.

Alpine Eco Trek, which offers guided tours and expeditions in Nepal, confirmed that 12 British nationals on its tour across the Nepal-Tibet border were missing on Wednesday.

Ram Kumar Adhikari, the manager of Alpine Eco Trek, said two Irish nationals and four South African nationals who were also on the excursion are believed to be missing.

Mr Kumar Adhikari said there was 'not much info to share at the moment, but yes we have 12 British citizens (supposed) to make entry this morning'.

The age of the missing British citizens ranges from 13 to 65, according to travel logs.

South Korea said eight of its citizens were unaccounted for, while an additional 12 were stranded following the deadly floods. 

The nationalities of nearly 100 more people have not yet been established, while an additional 37 people are believed to be non-resident Indians living in Nepal. 

Earlier today, the British embassy in Kathmandu said the UK was 'deeply saddened by the devastating flood which hit Rasuwa and other parts of Nepal this morning. Our thoughts are with all those caught up in this disaster.'

It added: 'We urge British Nationals in Nepal to follow official guidance and exercise caution in the affected areas.'

Meanwhile, a joint statement with the embassies of Australia, the EU, Finland, France, Norway and Switzerland read: '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.' 

Scientists are blaming an 'ice avalanche' for the disaster, in which massive chunks of dislodged ice blocked the Lhende river, causing water to build up before suddenly bursting downstream.

Rijan Bhakta Kayastha, a professor at Kathmandu University, said the area contains several large glacial lakes and the same river had been blocked in a similar way last year. 'The initial assessment this time is that an ice avalanche and possibly a glacial lake outburst caused the flood,' he told the Kathmandu Post. 

He suggested the ice avalanche happened in the Nepal side of the border, possibly connected to an earthquake recorded on the Tibetan side around the same time. 

Shanti Mahat, of the National Disaster Risk Reduction and Management Authority, said the agency had also received preliminary information that an ice avalanche had blocked a river.

An ice avalanche occurs when a large mass of glacial ice collapses down a steep mountain face. 

Unlike traditional snow avalanches, falling ice behaves similarly to a destructive rockfall due to its massive density and weight, often triggering severe flash floods if debris blocks local river systems.

Qianggong Zhang, head of climate and environmental risks at the Kathmandu-based International Centre for Integrated Mountain Development, warned the region may come under threat again. 

He said: 'With a blockage still lodged upstream on the Nepal-China border river, authorities warn a second flood may occur.' 

Search operations are currently under way on both sides of the border between Tibet and Nepal. 

At the Gyirong Port, authorities have deployed nearly 600 rescuers. 

But a rescuer told Chinese media that it would take at least four hours for the team to reach the site due to the five foot deep sediment that blocked pathways leading to the affected area. 

The debris had surged upstream from the Nepalese side of the crossing, the rescuer said.

The port normally sees hundreds of millions of dollars of good flow through every year, accounting for around a third of all of China's trade with Nepal. 

Last year, floods swept away the bridge connecting it to Nepal's Rasuwa Port, leaving trade through the port suspended for six months. 

The Nepal Army said 14 helicopters and disaster response teams have been deployed for rescue and relief. 

But officials said the waters were too high for helicopters to land in Nepal's affected areas of Syapru Besi and Timure in the mountainous district of Rasuwa, with a population of about 50,000. 

Nepal's rescue helicopters would be unable to land in the affected areas until the waters recede, however, army spokesperson Raja Ram Basnet said. 

'There could be heavy casualties or loss of property,' district administrator Narendra Pariyar told Reuters. 

'But I cannot say for sure now.' Pariyar urged those living on the banks of the Bhote Koshi river in the area to seek higher ground, pointing to reports that nearby villages and infrastructure project sites were washed away.

'It all came suddenly,' the Onlinekhabar portal quoted a witness from the area as saying. 'We heard a loud sound, like a volcano erupting. People started to scream and ran away.'

Around 60 houses in the Trishuli Bazaar area were swept away, while the nearby Devighat was also badly affected. Two bridges over the nearby Trishuli River were also washed away. 

Nepali media reported that 60 employees of an under-construction hydropower project are missing following the floods. 

Staff working at the Langtang Khola Hydroelectric Project in Rasuwa have not been accounted for. 

Local media reported that workers were 'carrying out concrete construction work inside a tunnel', adding: 'The flood caused severe damage to the project.'

Rasuwa is home to several hydropower plants. Nepal's energy ministry said 430 MW of electricity supplies were affected, mostly from hydroelectric projects, or more than 12% of total national hydropower capacity of 3.2 GW, a Reuters calculation showed. 

The mudslide on the Nepali side hit China's Gyirong port, cutting off roads, communications and power in the Shigatse region near the border with Nepal.  

'I witnessed the flood sweep away eight or nine trucks, along with houses and people,' Suman Chalise, a 34-year-old teacher, told AFP in Nuwakot district.

'It was absolutely heart-wrenching. I had not witnessed such devastation before.'

One Chinese businessman told the BBC that his logistics firm has seven container trucks in the area of the flash flood, which are all staffed by Nepalese employees. 

Yee Liang told the broadcaster: 'We have lost contact with all of them. There is no signal, so we cannot reach anyone.'

He said that, as far as he's aware, there was no warning prior to the disaster: 'There were occasional mudslides and landslides, especially in the rainy season, but this one seems much more serious.'

President Xi Jinping urged 'all-out' search efforts for the missing as well as stronger monitoring and early warning systems to prevent secondary disasters.

Prime Minister Balendra Shah said police and military were joining rescue and relief teams.

Meanwhile, Indian Prime Minister Narendra Modi said New Delhi was ready to provide all possible humanitarian assistance and teams from the two countries were coordinating closely on rescue and relief efforts. 

'Instructions have been given ... to move the people living in the lower areas to safer places,' he said. 'People along the river are advised to exercise extra caution and remain alert.' 

The Red Cross said this morning that it had activated emergency response teams, mobilised volunteers and was deploying an emergency team with relief supplies in response to the natural disaster. 

The Lhende Khola River, a tributary of the Bhotekoshi River, witnessed maximum flooding on Wednesday, experts at the Kathmandu-based International Centre for Integrated Mountain Development said.

'The Lhende Khola has flooded twice in fourteen months, this time triggered by an ice rock avalanche from a glacier on the Nepal side that blocked the river and released a sudden surge downstream,' said Saswata Sanyal, a disaster risk reduction specialist at the climate research group.

'In a warming Himalaya, early warning is the first line of adaptation,' he added.

Another expert at the centre warned that a second flood may happen. Qianggong Zhang, head of climate and environmental risks, said: 'With a blockage still lodged upstream on the Nepal-China border river, authorities warn a second flood may occur.'

From its origins in Tibet, the Bhote Koshi river empties into Nepal's Trishuli river that eventually flows into India as the Gandak river.

A deadly flash flood on the same river last year was eventually traced to the draining of a glacier lake. 

Last year's Bhote Koshi flood killed nine people, with 24 missing, as it washed away a 'Friendship Bridge' linking Nepal and China to disrupt trade and transport for months.

That flood was triggered by the draining of a supraglacial lake in Tibet. 

The Himalayan region, which crosses Nepal and several nearby countries including India, is especially vulnerable to heavy rains, floods and landslides because the area is warming up faster than the rest of the world due to human-caused climate change. 

Research has shown that extreme weather events including heat waves, heavy rains and melting glaciers have become more frequent in the region.

Researchers at the Kathmandu research group found earlier this year that glaciers across the Hindu Kush Himalaya region are melting at an accelerating rate, with ice loss rates doubling since 2000 primarily due to rising global temperatures and climate change.

The Daily Mail has contacted the UK's foreign office for comment.