Tropical storm Nisarga is likely to intensify into a severe cyclonic storm in the next 18 hours and make landfall close to India's financial and entertainment hub Mumbai tomorrow, the Indian Met department said today.

Authorities evacuated thousands of people from low-lying coastal areas of two states Maharashtra and Gujarat and federally-ruled territory of Daman and Diu on the coast of the Arabian Sea, reports our New Delhi correspondent.

The Indian Met department said the cyclonic storm, which is now a deep depression, is very likely to intensify in the next six hours and further into a severe cyclonic storm during the subsequent 12 hours.

The storm is likely to cross north Maharashtra state, whose capital is Mumbai, and adjoining south Gujarat coast tomorrow afternoon as a severe cyclonic storm with a maximum sustained wind speed of 100-110 kmph gusting up to 120 kmph, it said.

Nisarga, a name given by Bangladesh to the cyclone, may trigger a storm surge as high as two metres above the astronomical tide inundate the low-lying coastal areas of Mumbai, Thane and Raigad districts during the landfall, the Met department has said.

This would be the first cyclonic storm in more than a century to hit Mumbai which is reeling under a coronavirus pandemic having recorded over 41,000 cases so far.

"Nisarga is a severe cyclone and we're expecting a wind speed of 90-100 kmph, which I think is negotiable. Still, as a precautionary measure, we are going to start the evacuation of people from the coastal areas of the two states (Maharashtra and Gujarat) soon," National Disaster Reduction Force (NDRF) Director-General S N Pradhan said.

NDRF has deployed close to 1,300 of its personnel in Maharashtra, Gujarat and Daman and Diu to help evacuation efforts and for relief and rescue operations.

The storm may cause major damage to thatched houses, huts, power and communication lines and coastal crops, the weather department warned.

Nisarga comes after the recent Amphan cyclone that killed 99 people in West Bengal and affected lakhs of people in the state.