More than 250,000 people in Sri Lanka have been forced to flee after their homes were flooded.

Indian weather officials said there was a "possibility" that the deep depression over the southwest Bay of Bengal could develop into a cyclonic storm.

Cyclones -- the equivalent of hurricanes in the North Atlantic or typhoons in the northwestern Pacific -- are a regular and deadly menace in the region.

Having skirted the coast of Sri Lanka, it was now moving north towards India's southern Tamil Nadu state.

The India Meteorological Department said it was expected to hit India's southern Tamil Nadu and Puducherry coastline on Saturday morning as a "deep depression" with winds "gusting up to 70 kph (43 mph)".

Sri Lanka's Disaster Management Centre said some 276,000 people were seeking temporary shelter in public buildings after their homes were swamped.

The government has asked the army to help in relief operations.

The disaster centre said search teams were still looking for two missing children and two men, who were also swept away by flash floods while on tractor and trailer.

Deadly rain-related floods and landslides are common across South Asia, but experts say climate change is increasing their frequency and severity.