The King says he and Queen Camilla are “heartbroken” by the deadly flash floods near the Nepal-Tibet border, as 33 people from the UK are missing including a 13-year-old girl and 14-year-old boy.

The Prince and Princess of Wales also expressed their shock, saying they were “thinking of everyone caught up in this terrible disaster”.

The death toll from the floods has risen to at least 359, with more than 1,300 people missing, 644 of whom are tourists according to Nepali authorities.

Prime Minister Andy Burnham said the UK has offered £5m to help the Nepalese government following the floods, adding it was a “very distressing and devastating situation”.

King Charles said that he and the Queen were sending their “most profound sympathy to all those who have so tragically lost their loved ones”.

“Many in the United Kingdom have strong, deep and personal ties to this part of the world,” the King’s statement continued.

“We feel deeply for the many families awaiting anxiously the news of friends and relations.

“Our hearts go out also to the families of all the police and armed forces personnel who lost their lives while carrying out their courageous duty in the service of others.”

The prime minister and the Foreign Office in the UK have urged people to follow local guidance and remain alert to the changing situation, as officials in Nepal warn of a possible secondary flood risk near the Bhote Koshi river.

The Foreign Office added it was working closely with Nepalese authorities.

A British woman from Slough, Leena Bector, has been confirmed by Fishtail Tours and Travels as missing. Her husband, Bhupesh Bector, told the Times he is flying out to the country.

“I know that she’s in Nepal for sure, so even if they find her today or tomorrow, I need to be there,” he said.

British resident Pramod Pudel, who lives in East Sussex but is originally from Nepal, told BBC Radio Sussex on Thursday that “nothing remains” where his family lives and he is flying back to search for his wife, mother, brother and uncle.

“It’s a very, very difficult time for me and for my family and my country at this moment, but obviously I have to go and see what’s happening there,” he said.

“A lot of people are missing and there is no information regarding who is missing, where they are. Nobody can contact each other and all the bridges are broken, so you can’t cross the land.

“There’s no power, no electricity, so I can’t contact anyone, so it’s a very difficult time not knowing what’s happening.”

Essex nurse Rajendra Pudasaini said his relatives were “swept away” by the floods.

“My wife’s auntie and uncle, and their granddaughter and her husband are missing, and my godson as well,” he told PA Media.

“They’re gone. The speed the water came, they couldn’t be saved, they were just swept away.”

Meanwhile, a Nepalese man living in Aberdeen Barun Lamichhane, 26, told BBC Scotland News his brother, uncle and cousin all died in the disaster – but his mother, father and grandmother managed to escape.

Lamichhane said they got away by “crawling like a baby” into the hillside.

Other families are waiting for news, including Tatajana Phillips, from Folkestone in Kent, who said the last known location of her sister Julija Jakovicka was in the border area an hour before the flash floods struck.

“We are really hoping that people hear us and try to find and locate [my sister]”.

Phillips said her sister, a mother-of-two living in Germany, was in the country for a yoga and meditation retreat.

“We are terribly worried,” added Phillips’ husband Ben. “We just know where they were and that’s really tough.”

Tour companies including Alpine Eco Trek, The Trekkers’ Society, Himalayan Glacier US, Kailash Journeys and Fishtail Tours have reported missing British nationals while on trips with the companies.

Alpine Eco Trek said it has not been able to establish contact with 12 Britons who were booked on a tour to Mount Kailash and were in the region when the flash floods struck.

The company’s travel logs which were shared with the Press Association, with a 13-year-old girl the youngest person missing.

Four of the firm’s Nepali tour guides are also missing.

Mount Kailash – a peak in the Himalayas near the border between Nepal and Tibet – is considered the spiritual home of the Hindu god Shiva.

The journey to the mountain is part of the Kailash Mansarovar Yatra, a sacred pilgrimage for Hindus.

The pilgrimage had only recently resumed after being disrupted first by the pandemic and then by tensions between India and China.

The Trekkers’ Society said nine UK nationals on a pilgrimage to Mount Kailash are missing after they crossed the Nepal-Tibet border. Four males aged between 14 and 50, and five females aged 40 to 53 remain missing.

Himalayan Glacier US had 47 guests on a pilgrimage to Mount Kailash, with two in the group being British citizens.

Kailash Journeys reported 27 guests and staff were missing, with two British men in the group.

Fishtail Tours said one British person on its tour was missing.

The flood hit early on Wednesday in Rasuwa, just north of Nepal’s capital Kathmandu.

Preliminary information suggested it was caused by an earthquake, but the US Geological Survey said additional analysis indicated “the seismic energy was instead generated by a landslide.”

It said a magnitude 5.2 seismic event caused by a “glacial collapse and debris flow” occurred near the border at 08:37 local time on Wednesday.