At least 18 villages were washed away on Tuesday in flash flood in river Bhogdoi in the outskirts of the town affecting about 22,000 people.
Incessant rains in Nagaland and catchment areas of river Brahmaputra caused the water to swell in Bhogdoi, which is its tributary, and breach an embankment in the early hours of Tuesday, official sources said.
As the gushing water swept away the villages in the area, their about 22000 residents were evacuated to higher reaches.
The district administration has taken emergency measures to provide relief to the affected people, the sources said.
The area falls on the western side of this upper Assam town and grows large amounts of vegetables, they added.