Cyclone Phailin was expected to hit the impoverished states of Orissa and Andhra Pradesh on Saturday evening, accompanied by a storm surge of up to two and a half metres (seven feet) and heavy rainfall.
The storm "would increase in intensity with gale wind-speed reaching 205-215 kilometres (127-134 miles) per hour at the time of landfall", the Indian Meteorological Department said.
It warned of extensive damage to agricultural crops, homes and power and communication systems.
The army was on standby in both states for emergency and relief operations, the NDTV news network reported.
Choppers and food packages were ready to be dispatched in areas expected to be worst hit by the storm, which was one notch below the most powerful category.
State officials feared the wind speed could touch levels higher than that of a deadly super-cyclone that hit Orissa in 1999, killing nearly 15,000 people.
"We are fighting against nature.
We are better prepared this time, we learnt a lot from