COLOMBO: Heavy rains on Sri Lanka's coast and in the south Indian state of Tamil Nadu have killed at least 25 people, destroyed thousands of homes and snarled traffic, authorities said.

In Sri Lanka, 20 people have died in recent days, most from drowning, while five were hurt in landslides, officials said on Wednesday.

"Given the prevalence of COVID-19, the government has encouraged over a thousand families to move in with relatives to reduce the strain on government-run centres," said Sudantha Ranasinghe, head of Sri Lanka's Disaster Management Centre.

The low pressure depression behind the rains was expected to move towards Tamil Nadu on Thursday evening, Sri Lanka's weather office said. Five people have already died in the state whose capital Chennai is India's automobile manufacturing centre.

The Indian Meteorological Department issued a red alert to parts of Tamil Nadu and the neighbouring Andhra Pradesh state, asking fishermen not to venture to sea.

Tamil Nadu state officials evacuated hundreds of people from low-lying areas and distributed rations and food to those already affected by the rains.

The state's Chief Minister M.K. Stalin said on Twitter he had requested Prime Minister Narendra Modi to release funds from the National Disaster Relief Fund, adding that previously-allocated money was exhausted.