Taiwan authorities have said they received information about a possible terrorist attack on Beijing’s airport just four days before the Malaysian flight disappeared. They believe it is unrelated but are still investigating.

“Anything is possible. But I want to say that we should not jump to conclusions. However we do need to pay attention to any connections with this incident. We will make a judgment soon. A message was sent at that time saying Beijing’s airport was a target so we will need to check it out,” Head of Taiwanese Civil Aeronautics Administration Jean Shen said.

The search for missing Malaysian Airlines plane MH 370 with 239 people on board intensified on Monday.

Dozens of ships and aircraft from seven countries were scouring the seas around Malaysia and south of Vietnam.

There were hopes earlier that a floating yellow object could have been a life raft but Vietnam’s aviation authority said it had turned out to be debris.

What happened to the flight when it disappeared one hour into its journey from Kuala Lumpur to Beijing in the early hours of Saturday is a mystery.

Officials say they are not ruling out a bomb or hijacking attempt.

Interpol confirmed that at least two passengers used stolen Italian and Austrian passports. A spokeswoman said a check of all the documents used to board the plane had revealed more “suspect passports”, which were investigating.