A school principal who ordered an evacuation that saved 900 children in Nepal is being hailed a hero for his quick decision, as students described scrambling to safety with literally seconds to spare.

Rajendra Dawadi told children at Tribhuvan Trishuli Secondary School in Nuwakot to run to higher ground — 10 minutes before a wall of water slammed the town.

He told the BBC he had received warnings from four people within the space of minutes, which spurred him to act.

“A parent came and told me that a big flood was coming, ‘I am here to take my daughter, I will take her’,” he told the BBC.

“Parents don’t rush without a strong reason, so it was confirmed that I shouldn’t waste a second to evacuate the children.

“I decided I shouldn’t delay any more. Even if the flood was not coming, it was just a matter of a single day’s classes.

Dawadi added: “If we didn’t make a quick decision, if it was 10 minutes later, we all — including the students and me — wouldn’t be able to speak to you today.”

“I feel proud that we saved so many lives.”

Student Yunisha Amatya, 16, told the BBC she and her friends survived by “just 10 seconds” while scrambling to safety.

“Just before the flood came, we were in the class studying. Teachers had gathered in one place and initially had no idea what had happened,” she said.

“After five minutes, teachers came and informed us about the flood and asked us to go home.”

She said many students initially underestimated the danger and waited for classmates who were in a maths lesson.

Yunisha and her friends scrambled uphill through an escape route behind the school.

“I could not walk fast, and my friends helped me to climb uphill. We escaped through a narrow ladder from backside of the school,” she told the BBC.

“Within no time, the bazaar (a local market around the school) was swept away in front of my eyes.”

The Trishuli Bazaar area of Nuwakot district. Photo: AAP

“If there was no grip in my shoes I would have fallen, and students and other people were jostling each other to reach the safer area while escaping.

“The people who choose to escape from another route are apparently swept away.”

Authorities said the death toll rose to nearly 800 on Sunday, with more than 3000 people missing ‌on both sides of the Nepal-China border after a torrent of ice, rock, mud and debris swept through mountain valleys and rivers on Wednesday, causing widespread devastation.

The Red Cross has estimated that more than 90,000 people are likely to have been affected by ‌the disaster, which China has linked to the effects of climate change.

Chinese Foreign Minister Wang Yi told his Nepalese counterpart during a Saturday telephone call that the mudslide was the “most severe cross-border disaster” in recent years and that rescue operations had risen to an unprecedented level of difficulty and complexity, state broadcaster CCTV reported.

Sydney 26-year-old Cara Severino is safe and well in Nepal, according to her family.

Aussie families cling to hope

Family of Australians missing in the Nepal flood disaster are hoping for good news while facing a devastating reality.

The federal government has confirmed 42 citizens are among the nearly 3000 people still unaccounted for after the flash flooding.

In one miracle, formerly missing Sydney woman Cara Severino got in touch with her parents on Saturday and was safely located by Australian consular officials on the same day.

However, others remain unaccounted for. Renee Spry was making a pilgrimage with the Isha Foundation when the deadly inundation hit.

Her last known location was at an immigration office along the Nepal-Tibet border, the destruction of which was captured in widely shared footage.

Describing her sister as a deeply spiritual person, Clair Spry said Renee had long planned and looked forward to her journey to the pilgrimage site of Mount Kailash.

“Our family’s pretty realistic about what this is … everyone’s got that little sliver of hope that she is just stuck somewhere and helping and she can’t get to us,” Spry said.

“But then also, we’re very realistic, she was in the immigration centre 10 minutes before the wave hit.”

Prime Minister Anthony Albanese opened his remarks at Sunday’s Queensland Labor conference with a reflection for those caught up in the tragedy.

“That something so devastating could occur in such an awesome and inspiring corner of the world during times of pilgrimage and holiday makes the blow seem even more heartbreaking,” he said.

NSW mother-of-two Reshma Patel was travelling in the same group as Renee Spry when the wave struck the immigration centre.

Also on the tour were outdoor education leader Michael Keats, and mother Sumi Adhikari.

Adhikari’s wife Nava Pandey flew to Nepal following the disaster to find information about her whereabouts. But he said he still had no clear information about her status or that of other members of her group.

“Families should not be left without answers during such a critical time,” he said.

“Every hour matters.”

Jen Nai said her family was desperately waiting for news of her brother-in-law Karan Bhardwaj, who was travelling with friends Arpan Mithalal Kothari and Bhavin Raval as part of a tour group with Kailash Journeys.

Other Australians missing include 15 people who were on a trek with US travel company Himalayan Glacier Adventures, including two boys aged 11 and 14 and a Sydney couple with two sons in their 20s.

Tunnel rescues

Rescuers have worked around the clock since the glacier collapse unleashed a huge torrent of rock, ice, mud and debris on Himalayan communities.

Nearly 700 people have been confirmed dead following the tragedy, but the toll is expected to continue to rise rapidly as more bodies are uncovered.

The scale of the disaster has complicated rescue efforts across the rugged Himalayan terrain.

In Nepal, rescue efforts have increasingly focused on five hydropower projects inundated by the floods, including the Upper Trishuli complex, where authorities said on Friday they received information that about 350 people could be trapped inside a tunnel.

About 10,000 Nepali troops have been deployed alongside specialist teams from China and India.

Nepal’s military flew heavy machinery to the ⁠remote site on Sunday and rescuers reached the entrance of one tunnel, beginning to clear debris blocking access.

Authorities said teams carrying ‌oxygen supplies and cameras would ​enter once access was secured.

“It’s very tough because there’s a lot of debris and we cannot blast things to make our way through,” said Dharam Raj Uprety, chief of Nepal’s national disaster management authority.

-with AAP