At least five dead as 12-storey residential block falls in Alexandria.
Pandey said helicopters had been requested to help scour the river.
The 500-m long bridge was crowded with pilgrims headed to a religious ceremony to celebrate the full moon that began on Monday, Pandey said.
“The remoteness of the area and poor communication facilities have delayed rescue efforts,” he added.
The Himalayan nation is cut by dozens of rivers across one of the steepest topographies in the world.