His remark caused long delays for both his flight and the return flight from Chiang Rai, resulting in hundreds of passengers being left stranded at Suvarnabhumi Airport and Chiang Rai International Airport.

When the boy was about the board the Bangkok-Chiang Rai flight at 6.40pm on Sunday, he said he was carrying the bomb, causing security officials to search the plane.

The boy, whose name was withheld because he is a minor, was returning from the Philippines with a group of 31 students and teachers under a cultural exchange project.

He was carrying his belongings in both hands and his boarding pass was in the right pocket of his jacket. When a flight attendant offered to remove the boarding pass from his pocket he said: “Please be careful. There’s a bomb inside.”

The flight attendant, Manasnan Dongriengkaj, immediately informed the captain, who in turn alerted the security centre of Suvarnabhumi Airport. The boarding process was suspended immediately.

Passengers who had boarded the plane were evacuated and all bags were checked for an explosive.

The plane eventually took off at 11.20pm after being initially scheduled to leave at 6.45pm.

The delay caused a chain reaction that affected Thai Smile passengers waiting for the Chiang Rai-Bangkok flight scheduled to leave Chiang Rai at 8.30pm.

The returned flight eventually took off at 12.20am on Monday.

Passengers who had catch flight overseas were flown to Bangkok by other airlines.