An Alliance Air flight from Lilabari in Assam made an emergency landing at Calcutta airport on Sunday afternoon — one of nearly 25 flights that fell victim to bomb hoaxes through the day.

Close to 100 flights of Indian carriers including IndiGo, Air India, Vistara and Akasa Air have over the past week been delayed or diverted, or forced into emergency landings, because of false bomb alarms.

Many of these were international flights to and from countries ranging from Indonesia and Saudi Arabia to Turkey and Germany.

Bureau of Civil Aviation Security officials met airline CEOs online on Saturday to discuss the problem. Civil aviation ministry sources said strict action against the senders of bomb hoaxes was being planned, such as putting the callers on the no-fly list.

Officials said such a spurt in fake bomb alerts was very unusual but could not say whether these were pranks or had more sinister motives.

Alliance Air’s Lilabari-Calcutta flight, carrying 73 passengers, had taken off from Lilabari at 12.01pm, a Calcutta airport official said. Calcutta’s air traffic control received the hoax message shortly before the plane was to land.

“Full emergency was declared at 2.02pm for the flight,” the official said. The flight landed at around 2.15pm and was taken to the isolation bay.

“The frisking of the passengers and their hand baggage was completed at 3.05pm,” the official said.

Six IndiGo and six Vistara flights too were affected by fake bomb threats. Civil aviation ministry sources said several Akasa Air flights were also at the receiving end.

“We confirm receiving security threats, on social media, for six Vistara flights operating on 20 October 2024,” a Vistara spokesperson said.

The flights: UK25 Delhi to Frankfurt, UK106 Singapore to Mumbai, UK146 Bali to Delhi, UK116 Singapore to Delhi, UK110 Singapore to Pune, and UK107 Mumbai to Singapore.

“In line with the protocols, all relevant authorities were immediately notified and security procedures, as directed by them, are being carried out,” the spokesperson said.

An IndiGo statement identified the six flights that received security alerts as 6E87 Kozhikode to Dammam (Saudi Arabia), 6E11 Delhi to Istanbul, 6E112 Goa to Ahmedabad, 6E133 Pune to Jodhpur, 6E58 Jeddah to Mumbai, and 6E17 Mumbai to Istanbul.

Each of these planes was taken to the isolation bay and all passengers safely got off the plane, the airline said.

“We worked closely with the relevant authorities, and standard operating procedures were followed,” IndiGo said.

Air India too confirmed receiving security threats. “We confirm that some Air India flights operating on 20 October 2024 were subject to security threats received on social media,” a spokesperson said.

“Following the laid-down protocols, relevant authorities were immediately alerted,and all security procedures strictly adhered to, as per guidance from the regulatory authorities and security agencies.”

An official of an airline said the bomb hoaxes were causing passengers to feel harassed, delaying other flights across the targeted airlines’ networks, and triggering huge financial losses.