At least 160 people were killed in Nepal and hundreds more, most of them foreigners, were listed as missing on Wednesday in both Nepal and Tibet after flash flooding tore through border areas, according to authorities. The flooding was determined to have been caused by the collapse of a glacier, U.S. officials later said. 

The flash floods decimated villages, slamming into houses, roads, bridges and power plants. Videos broadcast by regional news outlets and posted on social media show violent torrents of water surging through valleys and mountain passes, tearing down bridges and dams and sweeping away buildings.

The Nepali police confirmed that at least 162 bodies were recovered following "devastating floods," but there was no word on the nationalities of the victims. Chinese state media reported "major casualties" from a mudslide at a Tibet border hub, including three dead.

Dozens of U.S. nationals were among the 341 foreigners listed as missing, according to Nepal's Tourism Board, citing information from tour companies.

Hikmat Singh Ayer, CEO and senior director of Nepal's Tourism Board, told CBS News that 403 people were unaccounted for after the flooding. He said that among the missing foreign nationals are 33 Americans, 34 Australians, 24 Canadians, 4 Germans, 19 Malaysians and one Israeli.

Chinese state broadcaster CCTV later reported that at least 558 people were believed to be missing on the Tibet side of the Nepal-Tibet border, according to The Associated Press. It said 260 of the 558 were foreigners. 

A sudden surge of water Wednesday morning in the Bhote Koshi River, in the country's northern Rasuwa district north of capital Kathmandu, quickly affected the neighboring Nuwakot and Dhading districts.

David Fisher, the head of delegation for the International Red Cross in Nepal, told CBS News that many areas remain inaccessible, hindering ground operations, but helicopter teams have been able to go in and rescue people.

"Entire villages have disappeared," Fisher said. "Markets have disappeared, and a critical artery for commerce between China and Nepal has also now been damaged, making it very difficult for many of those families who depend on that for their living."

Nepal's Foreign Minister Shishir Khanal initially reported that the flash flood was caused by an earthquake that triggered a large landslide, which blocked the Bhote Koshi River. 

However, the United States Geological Survey later reported that the flash flood was "instead generated by a glacial collapse and debris flow," stating that no earthquake occurred. 

"This event was initially reported as a magnitude 4.4 earthquake," the USGS said. "Additional analysis of nearby seismic stations, long period seismic waves, and satellite imagery led to the determination that the seismic event was instead a glacial collapse and debris flow, and that no earthquake had occurred."

Nepali President Ramachandra Paudel said he was "extremely saddened" by the "loss of lives and property caused by the sudden flood."

He called on the government, political parties, agencies and the general public to intensify rescue and relief efforts. 

"There could be heavy casualties or loss of property," district administrator Narendra Pariyar was quoted as saying by Reuters. He has also urged people living along the banks of the Bhote Koshi River to move to higher ground.

Nepal's mountainous terrain, dotted with deep valleys and narrow gorges, makes rescue and relief operations challenging. Helicopters could not land in the affected areas of Syapru Besi and Timure, Reuters said. 

Most of the missing foreigners were on trips organized by tourism and travel companies. 

The Nepal Electricity Authority (NEA) confirmed that six of its major hydropower and transmission facilities were damaged in the flooding.  

"We do not exactly know the extent of damage, but the flood is big, and it could have damaged many settlements," Nepal Police spokesman Abi Narayan Kafle told the French news agency AFP. "We have alerted people who are staying near the riverside to relocate ... and deployed all our resources."

In a social media post, U.S. Secretary of State Marco Rubio expressed U.S. solidarity with the Nepali people, saying his department "stands ready to support the government of Nepal with needed humanitarian assistance." 

The State Department said later Wednesday it would "provide $500,000 in assistance through its global award with Catholic Relief Services, supporting emergency shelter, relief items, and water, sanitation, and hygiene assistance to flood-affected communities."

The State Department also said its embassy in Kathmandu was working with local authorities to to find and help U.S. citizens affected by the disaster.

"Work has started to take necessary steps in coordination with the medical team, scouts, and Red Cross," Nepal's Prime Minister Balen Shah wrote in a social media post. 

India's government ordered authorities in states along the Nepal border to be on high alert.

Source: CBS News