A full emergency was declared at Thiruvananthapuram International Airport on Thursday after a bomb threat message was found in the washroom of an Air India flight arriving from Mumbai, according to airport sources.

The pilot of the aircraft informed the ATC about the threat after a 'Bomb in flight' message, written on a tissue paper, was found in the washroom of the plane, they said.

They also said that the police have initiated an investigation into the incident.

The aircraft is currently being inspected by security agencies, including a bomb detection squad, the sources said, adding that the passengers who travelled on the flight are presently waiting for their luggage to be delivered.

Meanwhile, Air India, in a statement, said that a specific security alert was detected on flight AI 657 during cruise from Mumbai to Thiruvananthapuram and "the crew carried out all the laid down security drills keeping passenger safety as top priority."

"All passengers and crew disembarked safely. Air India accords top priority to the safety of its passengers and crew," an airline spokesperson said.

The flight with 135 passengers landed safely at the airport around 8 am and was moved to an isolation bay, airport sources said earlier.

Passengers were safely evacuated from the flight by 8.44 am, they said.

The bomb threat was communicated by the pilot at 7.30 am as the aircraft approached the Thiruvananthapuram airport, the sources said.

Subsequently, a full emergency was declared at the airport at 7.36 am, they said.

"There has been no impact on life. Airport operations are currently uninterrupted," the sources said.