US investigators believe MH370 flew for hours longer than first thought based on data automatically downloaded and sent to the ground from the Boeing 777's engines.

US investigators believe MH370 flew for hours longer than first thought based on data automatically downloaded and sent to the ground from the Boeing 777's engines. Photo: Reuters

US investigators suspect the ill-fated Malaysia Airlines flight stayed in the air for about four hours after its last confirmed location, the Wall Street Journal reports, raising the possibility the search area for the plane should expand even further.

Two people familiar with the investigation told the publication's Asia edition that the plane may have flown for a total of five hours based on automatic data sent by the on-board monitoring system to engine manufacturer Rolls-Royce.

However, Malaysia's Acting Transport Minister Hishammuddin Tun Hussein has called the Wall Street Journal report "inaccurate" during a press conference at 8.30pm Thursday.

This shot from Boeing's website shows the equipment hidden beneath the engine's casing.

This shot from Boeing's website shows the equipment hidden beneath the engine's casing.

Malaysia Airlines chief executive officer Ahmad Jauhari Yahya said the engine's last transmission was 1.07am local time on the day the plane vanished.

"It did not run beyond that," he said.

The Wall Street Journal initially said they could not reach Rolls-Royce for comment but later updated the story with a response.

"We continue to monitor the situation and to offer Malaysia Airlines our support," a Rolls-Royce representative told the publication.

"The disappearance is officially not an accident and all information about this is strictly handled by investigators,” a Rolls-Royce executive is reported to have said. 

Also quoted was a Boeing executive who declined to comment except to say: "We've got to stand back from the front line of the information."

It was reported that live data from the plane's Trent 800 engines is recorded in 30-minute increments and sent to Rolls-Royce for analysis, with the information showing details such as altitude and speed of the jet.

Rolls-Royce says on its website that engine data is routinely used “so that plane operators can easily view the health of their fleet of engines”.

“Snapshots” are sent from the aircraft to the ground during take-off, during a climb, once the aircraft is in cruise and at the end of the flight – and are also triggered by unusual engine conditions, the website states.

“The snapshot data is always 'trended', so that subtle changes in condition from one flight to another can be detected.”

The comments revise earlier estimations that the plane flew for one hour and 10 minutes after it vanished from radar over the South China Sea, according to a Malaysian air force official quoted by CNN.

A total flight time of five hours means the Boeing 777 could have travelled about 2200 nautical miles after leaving Kuala Lumpur and potentially have reached the Indian Ocean, the border of Pakistan or even the Arabian Sea, the Wall Street Journal said.

The massive search for the plane has already expanded to an area of several hundred kilometres as Malaysia's military revealed it tracked a missing jetliner by radar over the Strait of Malacca on Wednesday.

However, Malaysia's civil aviation chief said no signs of the missing Malaysian plane have been found in an area where Chinese satellite images have shown what might be debris.

"This morning we sent two AN-26 aircraft to inspect the maritime areas near Con Dao island, where three suspicious objects were detected by Chinese satellite. Both have returned and we found nothing so far," Dinh Viet Thang, deputy director of Vietnam Civil Aviation Authority, said on Thursday.

The hunt for the Boeing 777 has been punctuated by false leads since it disappeared with 239 people aboard just hours after leaving Kuala Lumpur for Beijing early on Saturday.

The plane was heading east over the South China Sea when it disappeared, but authorities believe it may have turned back and headed into the upper reaches of the Malacca Strait or beyond.

smh.com.au with AAP