Thirty flights flying through the Calcutta air traffic control’s route were diverted because of Cyclone Amphan, airport sources said on Wednesday.

Flight operations are closed at the Calcutta airport because of the lockdown. International flights from one country to another fly over the city’s sky and are controlled by the air traffic control of Netaji Subhas Chandra Bose International Airport.

There are several routes under Calcutta’s air traffic control.

According to an official, aircraft flying over at least three such routes had to be deviated because of Amphan.

“Those flying over Bhubaneswar and the Bay of Bengal were diverted through Dhaka and Varanasi,” said an airport official.

He said though these overflying flights fly at a height between 33,000ft and 41,000ft, which is much higher than the height of the cyclone, they have to fly through a route to ensure they can land in case there is an emergency.

Because of Cyclone Amphan, Calcutta airport announced that it would remain closed for any take-off or landing till 5am on Thursday.

There are around 200 flights flying over Calcutta, mostly between countries connecting Southeast Asia, Australia and Far East with Middle East and Europe.