Nepali army helicopter rescue teams were working on Friday to rescue around 100 people trapped inside a tunnel at a hydropower project swamped by a devastating flood two days earlier.

"Our focus is in search and rescue of people... some people are trapped in the tunnel of Trishuli 3A hydropower project," Nepal Army spokesman Raja Ram Basnet said.

"Two helicopters have been dispatched but it is challenging because it is tough to even locate the entry points of the tunnel. Relief efforts are also underway to provide the rescued people what they need."

The country's prime minister's office said in a statement that the army had been working in tough conditions.

"A Nepali Army team has successfully rescued 350 workers and locals who were trapped in the tunnel a while ago facing extremely risky and challenging conditions amid adverse weather and rapid floodwaters," the statement read.

"The army is still working to safely evacuate more than 100 people trapped in the same tunnel."

It did not give further details about the nationalities of those rescued or trapped.

The scale of destruction from devastating floods in Nepal's northern border region was becoming clearer on Friday, with roads, bridges and hydropower infrastructure destroyed and survivors describing scenes of extraordinary devastation.

Workers rescued from other dam projects along the Trishuli valley described a disaster that unfolded with terrifying speed.

"There were at least 400 workers at the site," Dev Shrestha, who was airlifted from the site where he was working, said after his rescue. "More people died than were rescued." (AFP)


Edited by Aaron Tam