There had been no heavy rainfall in the immediate area of the river in the preceding 24 hours, but weather forecasting experts said Tuesday's flood might have been the result of an overflowing glacial lake in Tibet, where torrential rain had fallen.
Police had recovered eight bodies, none of whom had been identified so far, Nepal Police spokesperson Binod Ghimire told Reuters.
He said 57 people were rescued. Search and rescue operations were continuing, Nepali Army spokesperson Raja Ram Basnet said.
At least 20 people were missing in Nepal, while China's official Xinhua news agency said 11 people were unaccounted for on the Chinese side of the mountainous border region.
Trade between Nepal and China was disrupted because of the bridge's destruction, officials said.
In Nepal, the missing included six Chinese workers and three police personnel, the National Disaster Risk Reduction and Management Authority (NDRRMA) said on X.
The missing Chinese nationals were working at the Inland Container Depot being constructed with Chinese assistance about 80km north of capital Kathmandu, said Arjun Paudel, a senior administrative official of Rasuwa district.
"The river also swept away some containers with goods imported from China... There is a big loss (of property) and we are collecting details," he told Reuters.
China has been increasing its investment in Nepal in recent years in domains including roads, power plants, and hospitals.
The Asian giant has been battered by heavy rain and flash floods over the last few days that have left a trail of destruction, and is bracing for a tropical storm this week.
Nepal's weather forecasting department said it was working with Sentinel Asia - an international initiative that uses space-based technology to support disaster management in the Asia-Pacific region - to determine the cause of the flooding.
In Pakistan, at least 79 people, including 38 children, have died in floods and rain-related incidents, including landslides and house collapses, since June 26, its National Disaster Management Authority said on Tuesday.
The authority issued fresh alerts for flash flooding and glacial lake outbursts in the northern and northwestern provinces of Gilgit-Baltistan and Khyber Pakhtunkhwa, citing "a significant rise in temperatures and... an upcoming weather system."
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