A bomb hoax delayed by three hours the departure of a special Indian Air Force aircraft carrying President A P J Abdul Kalam to New Delhi.

The flight, which was scheduled to leave at 11 pm on Monday night, took off from Chennai at 2 am on Tuesday after security agencies, aided by sniffer dogs and bomb disposal squads, conducted a thorough check and gave the green signal to fly, airport sources said.

An anonymous caller had rung up the police control room claiming a bomb was planted in a Tamil Nadu government aircraft by which Governor S S Barnala was to travel, police said.

But since the governor had no travel plans and the President's special aircraft was scheduled to leave, the authorities took no chances and thoroughly checked the IAF aircraft berthed at the base seven of Meenambakkam airport.

Police said the caller spoke in Tamil and efforts were on to trace him.

The call came when the President, who attended a series of functions in Chennai through the day, was talking to his relatives, who had come to meet him from his native place Rameswaram, well after the ceremonial send-off by the governor.

Director General of Tamil Nadu Police D Mukherjee said the PCR at Egmore in Chennai got the call at around 10.30 pm claiming that a bomb had been planted in a state government flight.

"The police did not want to take any chances. We conducted a thorough check and found no explosives or bombs," he told reporters soon after the flight took off from Chennai.

The police were making all efforts to trace the caller, City Police Commissioner Latika Saran, who was also present at the airport said.

Soon after the call came, all top police officials rushed to the airport, Saran added.