Security has been beefed up at Mumbai international airport following bomb threats. The airport security received the first threat on Monday night. This was followed by three more phone calls on Tuesday reiterating that the airport will be blown up in 24 hours.

"The calls have been traced to a PCO in Kalyan. We have sent a team for further inquiry," said a policeman attached to the additional commissioner of police office, Mumbai airport zone.

Meanwhile, security personnel at the airport are on a state of high alert. Extra patrol has been deployed in the perimeter of the airport, extra security men have been posted at the entry points and vehicles entering the airport are being thoroughly checked. Security personnel have been instructed to intercept and frisk any suspicious-looking individual or vehicle.

"We are thoroughly checking the passengers and their belongings. Bomb disposal squad personnel and six extra units of security personnel and Central Industial Security Force men have been deployed in the airport," the policeman said.

However, the police believe the threat is likely to be a hoax. A similar threat was received last week about the World Trade Centre in Cuffe Parade, South Mumbai and Film City in Goregaon, which turned out to be false alarms.

"We are not taking this threat lightly. We have traced the location of the call and also the team dispatched has got further information regarding the matter. Hoax or no hoax, we are on full alert," said another police official.