Indian authorities closed schools and colleges on Monday and prepared to move people out of low-lying areas as a cyclone bore down on the southeast coast.
Cyclone Vardah is moving westwards over the Bay of Bengal and is expected to hit the city of Chennai and neighbouring areas Tamil Nadu state within the next few hours, the Indian Meteorological Department said.
Rain began battering the densely populated coast ahead of the storm's landfall.
Vardah is forecast to weaken gradually as it moves west but wind speeds are still predicted to hit about 100 kph (62 mph) and rain will be very heavy when it reaches land.
A "storm surge" will be about one metre (three feet) high.
The National Disaster Management Authority advised fishermen to avoid the sea in the states of Tamil Nadu and Andhra Pradesh for the next 36 hours, and told residents to stay in safe places.
Navy ships and aircraft, as well as 30 diving teams, were on standby to help move people and deliver aid if need be, a navy spokesman said.
India's cyclone season usually lasts from April to December, and storms often cause dozens of deaths, evacuations of tens of thousands of people from low-lying areas and widespread crop and property damage.