Schools and ports have shut down in southeast India as Cyclone Nilam heads towards the coast, with landfall expected on Wednesday evening.
Authorities said thousands of people had moved to higher ground as the cyclone could cause a tide surge of up to 1.5m and flood low-lying areas of Tamil Nadu and Andhra Pradesh states.
The meteorological department said the cyclone was expected to damage thatched huts and uproot trees, knocking out power and communication lines across the two states.
Heavy rain has already started, lashing the region.
Chennai, the state capital of Tamil Nadu, is in the middle of the affected zone.
Local authorities said they were preparing helicopters and boats for any emergency. Existing cyclone shelters, schools and community halls have also been identified to serve as potential relief camps.
Neighbouring Sri Lanka on Tuesday allowed thousands of people who had been evacuated to return to their homes after the storm, which had been expected to hit the island, changed course and moved towards India.
The last cyclone in India struck in the same southeast region in January, claiming 42 lives and leaving a trail of destruction across Tamil Nadu.
India and Bangladesh are hit regularly by cyclones that develop in the Bay of Bengal between April and November, causing widespread damage to homes, livestock and crops.
India's Andhra Pradesh state saw its worst cyclone in 1977 when more than 10,000 people were killed.