The last words from the cockpit of a missing Malaysia Airlines jet were a standard "Goodnight Malaysian three seven zero", Malaysian authorities have said.

That changes its account of the critical last communication from a more casual "All right, good night".

The correction more than three weeks after Flight MH370 vanished with 239 people on board was made as Malaysian authorities face heavy criticism, particularly from China, for mismanaging the search and holding back information.

Malaysian authorities released the transcript of communications between the cockpit crew and air traffic controllers, saying the exchanges showed nothing untoward.

"There is no indication of anything abnormal in the transcript," a statement by Defence and Transport Minister Hishammuddin Hussein said.

Painstaking analysis of radar data and limited satellite information has focused the search on a vast swath of the southern Indian Ocean west of the Australian city of Perth, but has so far failed to spot any sign of the plane.

Search coordinators warned the hunt could drag on for some time yet.

"In this case, the last known position was a long, long way from where the aircraft appears to have gone," retired Air Chief Marshal Angus Houston, the head of the Australian agency coordinating the operation, told reporters in Perth.

"It's very complex, it's very demanding and we don't have hard information like we might normally have," he said.

The Boeing 777 disappeared from civilian radar in the early hours of 8 March as it flew from Kuala Lumpur to Beijing.

Its communications were cut off and it turned back across Malaysia and headed towards the Indian Ocean.

Malaysia says the plane was likely diverted deliberately, probably by a skilled aviator, leading to speculation of involvement by one or more of the pilots.

Investigators, however, have determined no apparent motive or other red flags among the 227 passengers and 12 crew.

"We would like to confirm that the last conversation in the transcript between the air traffic controller and the cockpit is at 0119 (Malaysian Time) and is "Good night Malaysian three seven zero," the Department of Civil Aviation said in a statement.

Malaysia's ambassador to China told Chinese families in Beijing as early as 12 March that the last words had been "All right, good night".

About two-thirds of the passengers on board were Chinese.

The department said authorities were still conducting "forensic investigation" to determine whether the last words from the cockpit were by the pilot or the co-pilot.

Malaysia Airlines had previously said the words were believed to have come from the co-pilot.

Elsewhere, nine ships and ten aircraft resumed the hunt for wreckage from MH370 this morning.

They are hoping to recover more than fishing gear and other flotsam found since Australian authorities moved the search 685 miles (1,100km) north after new analysis of radar and satellite data.

Mr Houston said the challenging search, in an area the size of Ireland, would continue based on the imperfect information with which they had to work.

"But, inevitably, if we don't find any wreckage on the surface, we are eventually going to have to, probably in consultation with everybody who has a stake in this, review what to do next," he said.