Malaysian police are investigating a flight engineer who was among the passengers on the missing Malaysia Airlines plane as they focus on the pilots and anyone else on board who had technical flying knowledge, a senior police officer said.

The aviation engineer is Mohd Khairul Amri Selamat, 29, a Malaysian who has said on social media he had worked for a private jet charter company.

"Yes, we are looking into Mohd Khairul as well as the other passengers and crew. The focus is on anyone else who might have had aviation skills on that plane," a senior police officer with knowledge of the investigations told Reuters .

Malaysian investigators are trawling through the backgrounds of the pilots, crew and ground staff who worked on the missing Boeing 777-200ER for clues as to why someone on board flew it hundreds, or perhaps thousands, of miles off course.

No trace of the plane has been found more than a week after it vanished but investigators believe it was diverted by someone with deep knowledge of the plane and of commercial navigation.

Prime Minister Najib Abdul Razak said on Saturday evidence pointed to a deliberate diversion of the flight, given the controlled way it was apparently turned around and flown far to the west of its original route from Kuala Lumpur to Beijing.

A flight engineer is responsible for overseeing systems on a plane during flights to confirm they are working correctly and to make repairs if necessary. As an engineer specialising in executive jets, Khairul would not necessarily have all the knowledge needed to divert and fly a large jetliner.

Khairul had said he worked for a Swiss-based jet charter firm called Execujet Aviation Group, but the company declined to say whether it still employed him.

In a picture posted on Khairul's Facebook account in 2011, he identified himself as an employee of Execujet's Malaysian operations.

"We can't disclose anything. We want to protect the family's privacy," an officer at the company's Malaysian office said.

Khairul, a father of one daughter, had recently bought a house on the outskirts of Kuala Lumpur and has more than 10 years experience as a flight engineer, his father Selamat Omar told Reuters .

Selamat declined to say whether he believed his son could have been involved in any foul play.

He said he and other family members were supposed to visit Khairul's new house this month.

However, Khairul had told his father on on March 6 that he had to go for a job in Beijing and that they would reschedule. That was the last time they spoke.

"Khairul was doing well in his job and was a good son. He would come visit us at least once a month," Selamat said.

- Reuters