Three major international airports in India have been placed on high alert after a reported hijack threat. Paramilitary forces are on standby and full-scale anti-hijack drills are underway at the facilities.

An email message received for the airports in Mumbai, Chennai and Hyderabad warned of "simultaneous" hijack attempts. A woman had reportedly heard six men speaking about hijack plans at a restaurant and alerted the authorities, it was reported.

Soon after the Mumbai police received the alert, they alerted the Central Industrial Security Force (CISF), which oversees airport operations across the country. Parking areas and entry points are being thoroughly checked.

"The email could well be a hoax, but we didn't take any chances. Embarkation (boarding) security increased, the anti-contingency plan put in place and meeting of all stakeholders held," O P Singh, Director General of the CISF, said.

The alert level is similar to what it is when India marks key national days such as Independence Day or Republic Day. Specifics of the threat perception are being withheld by authorities. "Yes, there is an alert, and we have implemented all the contingency measures, which cannot be disclosed. This is a standard procedure - whenever there is a threat perception or a threat alert, we implement it," G Chandramouli, Chennai Airport Director, told the News Minute.

Special anti-sabotage sweeps were carried out by counter-terrorism forces both on Saturday, 15 April, night and on Sunday morning. Airlines have been urged to remain extra-cautious, and sniffer dogs have been brought in as part of the sanitisation drills.

Airline operators have asked passengers to check in early in line with the security situation.

India experienced a hijack situation in 1999 when Pakistan-based militants hijacked a passenger plane to Kandahar. The government was forced to release three terrorists in exchange for 166 hostages.