Bangladesh has evacuated nearly 800,000 people from vulnerable areas as the country and neighbouring India awaited the arrival of a severe cyclone that has formed over the Bay of Bengal.

The storm is expected to cross Bangladesh and India’s West Bengal coasts around midnight on Sunday.

The India Meteorological Department said it is expected to reach maximum wind speeds of up to 75 mph, with gusts up to 85mph hitting West Bengal’s Sagar Island and Bangladesh’s Khepupara region on Sunday night.

Bangladesh’s junior minister for disaster management and relief, Mohibur Rahman, said volunteers have been deployed to evacuate people to 4,000 cyclone shelters across the country’s coastal region.

The government also closed all schools in the region until further notice.

India’s Kolkata airport will be closed for 21 hours from midnight on Sunday. Bangladesh shut down the airport in the south-eastern city of Chattogram and cancelled all domestic flights to and from Cox’s Bazar.

Bangladeshi authorities also suspended loading and unloading in the country’s largest main seaport in Chittagong and started moving more than a dozen ships from the jetties to the deep sea as a precaution.

This is the first cyclone in the Bay of Bengal ahead of this year’s monsoon season, which runs from June to September.

Moderate to heavy rainfall is expected in most places over coastal districts in India’s West Bengal state. A storm surge about one metre high is expected to flood low-lying areas of coastal West Bengal and Bangladesh.

Such storms can uproot trees and cause major damage to thatched homes and power and communication lines, the statement said.

India’s coasts are often hit by cyclones, but changing climate patterns have caused them to become more intense, making preparations for natural disasters more urgent.