Families are rushing to Nepal to search for the 33 British nationals who are still missing, as fears mount over the risk of a second wave of flooding in the region.

The catastrophic flash floods that hit Nepal and Tibet on Wednesday, thundering down valleys and sweeping away entire villages, have killed at least 538 people, while more than 1,500 remain missing.

Among them are hundreds of foreign tourists who were visiting the mountainous region, which is popular with trekkers and pilgrims for its natural beauty and religious significance.

Relatives of missing Britons have shared their devastation as they desperately try to reach their loved ones who were last seen in the Rasuwa district, where power and communication lines are down. Many are scrambling to book flights to Kathmandu, the Nepalese capital.

On Friday, authorities in Nepal and China issued warnings about the risk of a second wave of flooding. Chinese authorities said an artificial lake formed after a mudslide hit the Tibet-Nepal border, which risked “sending flood waters downstream”, according to state media. Nepal’s disaster authority said a lake formed by debris blocking a river at the flood site was also rising and ‌at risk of bursting.

Rescuers were forced to suspend their search for survivors, while residents who had returned to Rasuwa were told to evacuate their homes, with many seen fleeing up the hillsides to escape a possible surge in the river.

In a video on YouTube, Jaggi Vasudev, known as Sadhguru, a spiritual leader who founded the nonprofit Isha Foundation, told followers at the foundation’s camp at Saga in Tibet, China, that 80 members of an Isha group returning from Kailash Mansarovar, a high-altitude site in ‌Tibet revered by Hindus and Buddhists, were missing, including nine British people.

Among them is understood to be Neetu Goyal Tiwari, 51. Her brother Naresh Goyal told the BBC that completing the pilgrimage was “her dream”.

Fishtail Tours and Travels has confirmed Leena Bector, 53, from Slough, was among 27 travellers in its group who remain unaccounted for.

Her husband, Bhupesh Bector, told the Times he was booking the next flight to Kathmandu after the Home Office failed to confirm whether Leena was on its missing persons list. “Even if they find her today or tomorrow, I need to be there,” he said. “She must be in trauma.”

Also confirmed missing is Sarada Simkhada, a senior nurse from Dartford, Kent, who left for Nepal last Saturday on a religious journey.

Vikram Kolagatla, from London, told the BBC he had not heard from his wife, Geetha Reddy. Reddy, who has two daughters aged 12 and 14, had been in Hotel Kailash in Rasuwagadh when the flooding hit.

“We’re not sure what to do. I have two little girls, and their schools are starting next week,” Kolagatla added.

Tatjana Phillips, from Folkestone in Kent, told the BBC she had not been able to contact her sister, Julija Jakovicka, who was attending a yoga and meditation retreat near the Nepal-Tibet border when flash flooding hit.

The tour operator Alpine Eco Trek said it had been unable to make contact with a party of 12 Britons aged 13 to 65 who had booked a tour to Mount Kailash in Tibet, and were in the vicinity when the flash floods hit.

Sunil Amin, from Croydon in south London, shared with the Daily Mail the “horrible, horrible feeling” of repeatedly trying to phone his wife, Hema Amin, 63, who was on a pilgrimage with Alpine Eco Trek from Nepal to Tibet with her sister. “I’m devastated,” he said.

The Mail also reported that a family of four from Surrey, including a 13-year-old girl, were on the same tour that crossed into Tibet at the moment disaster struck.

The Trekkers’ Society, which organises tours across Nepal, Tibet and Bhutan, said nine UK nationals on a pilgrimage had gone missing. The organisation confirmed that four males, aged between 14 and 50, and five females aged 40 to 53 were unaccounted for.

Himalayan Glacier US said it had lost contact with a group of 47 guests and staff, including two Britons, who were also on a pilgrimage to Mount Kailash, regarded as the spiritual home of the Hindu god Shiva.

The tour operator Kailash Journeys confirmed it had not been able to account for seven UK nationals – five women and two men aged between 18 and 55 – travelling with it.

Twelve of the missing British citizens were on a tour to Mount Kailash led by Nabhi Nandan Das, a 64-year-old Hindu priest who works at the Sanatan Mandir and Community Centre in Surrey, the Telegraph reported. He is understood to have been leading 11 Britons on a tour that was due to visit Kailash and Lake Mansarovar, two Hindu holy sites in Tibet.

Pramod Poudel, who runs a Nepalese street food company in Sussex, told the Daily Mail his wife, Sumitra, mother, Tulisa, brother Pradip and uncle Madav were all missing. His father, Purusottam, has been found alive.

The Non-Resident Nepali Association in the UK launched an emergency fundraising appeal on Thursday and more than £12,000 has been raised.

Rajendra Pudasaini, a nurse in Essex who is president of the Non-Resident Nepali Association UK, said Nepal was witnessing an “irreplaceable loss” and the country was “paying the price for global warming”.

Pudasaini told BBC Radio 4 Today’s programme that many of his family members were missing. “My godson, we found the body yesterday morning, you know, he (was) just buried under the mud at his house, and yes, lots of other dead bodies being found.”

He added: “It’s a very difficult situation to describe, actually.”