Flood-ravaged Nepal is bracing for a second potential disaster as two lakes that developed on either side of the Nepal-Tibet border after Wednesday’s catastrophe threaten to burst.

Nepal and China have warned of the fresh risks of flooding in the Himalayas as the death toll rose to 362, with 1500 missing including 34 Australians.

Both countries have blamed the flood on a glacier collapse that pushed rock, ice, mud and debris into river systems in the mountains.

Adding to the shock, Nepal’s disaster authority issued a notice on Thursday (local time), warning that a lake formed by debris blocking a river at the flood ‌site is rising ‌and at ⁠risk of bursting.

“Residents of the lower banks … passengers, rescuers engaged in rescue operations, ​and all concerned are requested to exercise special caution and stay in safe places away from the river banks and risky areas,” the authority said.

China warned that three million cubic metres of water — the equivalent of about 1200 Olympic swimming pools — are expected to flow into an already dammed lake on its side of the border over the next three ⁠days, creating a high risk of a breach, with peak ‌flow expected ​on Tuesday.

The formation of a barrier lake was captured in aerial footage by a Chinese rescue team ​on Thursday, state ‌broadcaster CGTN reported.

The footage showed masses of brown water accumulating in a basin with no visible outlet.

The ​water had already submerged bushes and trees and appeared to push against a barrier of debris and stones.

Rainfall forecast over the coming week will exacerbate the threat, Chinese state media said, citing the ​Chinese ​water resources ministry.

“The volume of water is continuing ​to increase, and so is the risk,” Zhu Jinfeng, a ‌researcher at the water resources ministry’s hydrology department, told state broadcaster CCTV.

Fears for ‘lovely’ Australians

Sydney brothers Aarush and Ashwin Muralitharan were on a tour with their parents. Photo: Supplied

Some of the 34 Australians missing in northern Nepal have been named, including brothers Aarush and Ashwin Muralitharan, 11 and 14, who were travelling with their parents.

Other Sydneysiders named as unaccounted for are Sridharan Iyer and Lakshmi Iyer and Rudhra and Rishab Iyer.

Loved ones are hoping to hear from dozens of Australians, including a “lovely” group of family friends undertaking a sacred pilgrimage.

Fifteen Aussies were undertaking a trek with US travel company Himalayan Glacier Adventures.

Vasan Srinivasan, who knows 14 Australians on the tour, said the group were family friends completing a sacred pilgrimage together.

“Hopefully we find them somewhere safe … I’m just praying every minute,” the Confederation of Indian Australian Associations chair told AAP.

The Hindu Indian families from Sydney and Melbourne were active community members who frequently volunteered for causes including mental health awareness.

“They are lovely families, the kids are all studying and they are all very connected to the community,” Mr Srinivasan said.

“I’m a bit shaken up, they are 14 of my close family friends.”

Earlier on Thursday the tour operator said it had not been able to contact anyone from the group, which included two boys aged 11 and 14, because of damage to mobile networks and electricity infrastructure.

Chief executive Sagar Pandey flew by helicopter to “personally observe the situation and aid with rescue” but was unable to land becaujse of conditions on the ground, the company said.

The tour group took off from Kathmandu on Sunday for a 13-day trek to the sacred Mount Kailash and Lake Manasarovar on the Tibetan Plateau.

Photos posted on social media in recent days showed the Australians smiling upon arrival at Kathmandu Airport and receiving safety briefings.

The Himalayan Glacier website lists “possible landslides on the Nepal side” during tours in August.

Some communities tried in the seconds they had to warn people downstream of the impending flood, University of Sydney disaster management expert Soniya Rijal said.

“People were informing their relatives and neighbours via call saying, ‘the flood is coming, please be careful, evacuate’,” she told AAP.

“However, people did not believe it because it wasn’t raining. They thought they would be okay.”

The Nepalese Embassy in Canberra said efforts to locate and rescue those affected, and assess the full extent of human casualties and damage, were ongoing.

-with AAP, AP and DPA