Heightened tensions between India and Pakistan meant summer holiday plans going haywire for many.

India has closed 27 airports in northern, western and central India. A dozen flights to and from Calcutta were cancelled on Thursday, said airport officials.

Domestic flights from cities like Amritsar, Hindon, Chandigarh and Srinagar were cancelled. A couple of international flights, from Chittagong and Dhaka in Bangladesh, were also cancelled.

Calcutta’s air traffic control has had to tweak plans like other ATCs in the country to divert flights that usually fly over Pakistan’s airspace.

The required separation between two aircraft has now been reduced on these diverted routes to accommodate more traffic, said sources in the ATC.

“International flights going through Lucknow onwards to Pakistan are now being diverted through Jabalpur, Bhopal and Mumbai. So, these routes have more traffic than usual,” said an airport official.

Usually, the longitudinal separation between two aircraft is 50 to 80 nautical miles or 93 to 148 kilometres. Now, on the routes where the diverted aircraft are flying, the longitudinal separation has been reduced to 20 nautical miles or 37 kilometres, said sources.

The cancellations, diversions, closure of airports and blackouts in several cities have made travellers apprehensive, said tour operators.

Ratan Lal Shaw, 69, a resident of Talatala, was excited about a nine-day trip to Kashmir later this month. He would have left the city with his wife on May 20. The itinerary included Srinagar, Kargil, Dras, Leh and Ladakh. But the couple have now decided to abandon the plan.

“Our son, daughter-in-law, daughter and son-in-law have put their foot down. They will not let us go in this volatile situation,” said Shaw, an advocate at the city civil court. He had made advance payments for the trip, organised by a city travel agency. “We will get a refund,” he said.

Santanu Pathak, a doctor, has a 10-day trip to Ladakh planned from May 20.

“I have not called off the trip as of now. But by the looks of it, I may have to cancel it,” said Pathak. He is slated to be part of a larger group. “I will discuss with the agency and other travellers before taking a final call,” he said.

Raktim Roy, managing partner of Dolphin Travels, said he has at least six groups scheduled to visit places like Ladakh, Himachal Pradesh and other places in north and central India.

“We are yet to call off the tours. We are waiting for further developments,” said Roy.

“However, there are apprehensions among many members of these groups and several have called us to cancel,” he said.

“Apprehensions and fear are triggering cancellations and rebookings,” said Anil Punjabi, national committee member of the Travel Agents Federation of India representing the eastern region.