At least 332 people are dead and more than 1,500 remain missing after a catastrophic glacial collapse triggered flash floods along the Nepal-Tibet border on Wednesday, with rescue officials putting the odds of finding survivors at just 1 percent.

Nepal police issued the latest toll at 3:50pm local time on Thursday, a day after walls of water and debris tore through villages across a 40 to 50km stretch of the Himalayas, wiping out settlements entirely, reports The Independent.

Among the missing are 33 British tourists, including a 13-year-old girl, as well as nearly 800 foreign nationals in total.

Bishal Nath Upreti, president of the Nepal Centre for Disaster Management, described the disaster as a "tsunami from the sky."

Scientists believe a massive chunk of glacial ice broke away and temporarily blocked a river, causing water to build up before surging downstream with devastating force hours later.

The US Geological Survey recorded a magnitude 5.2 glacier collapse, confirmed through seismic data and satellite imagery.

Jakob Steiner, a geoscientist at the University of Graz currently based in Bangladesh, said the lower section of a glacier had sheared away entirely.

"If you look at the imagery, it's like someone cut with a huge knife through the whole lower part and it fell off," he said, adding that the impact of glacial ice falling from such a height could have felt like a bomb detonating.

Investigators are still analysing satellite and ground-level data to establish a precise sequence of events.