Media playback is unsupported on your device Media caption Nurlaila Binti Ngah, wife of chief steward Wan Swaid Wan Ismail: "We just wanted our husbands back"

Malaysia Airlines has asked relatives of passengers on board flight MH370 to leave the hotel accommodation it is providing and return to their homes.

It is closing the family assistance centres set up after the plane vanished on 8 March with 239 people on board.

The airline promised to keep relatives updated on the search operation.

Meanwhile, a report by Malaysia's transport ministry has shown a four-hour gap between MH370's disappearance and the start of a search operation.

The report also revealed that air traffic controllers did not realise the plane was missing until 17 minutes after it disappeared off radar.

The plane disappeared over the South China Sea as it flew from Kuala Lumpur to Beijing.

Officials believe it ended its journey in seas west of the Australian city of Perth, thousands of kilometres off course, but do not yet know why. An intensive multinational search has so far turned up no sign of the plane.

'Unimaginable anguish'

On Thursday, Malaysia Airlines said in a statement on Thursday that despite "probably the largest (search) in human history... the fate of the missing passengers and crew remains unknown".

Image copyright AP Image caption The families have been critical of the initial search process and the way they have been kept informed

Image copyright Reuters Image caption The Australian head of the search operation has said it could take as long as a year

"Malaysia Airlines is acutely conscious of, and deeply sympathetic to the continuing unimaginable anguish, distress and hardship suffered by those with loved ones on board the flight."

But it warned that the continuing search would be a "prolonged process".

"Instead of staying in hotels, the families of MH370 are advised to receive information updates... within the comfort of their own homes."

All family assistance centres would be closed on 7 May, but the relatives would be given updates through telephone calls, messages, the internet and face-to-face meetings, Malaysia Airlines said.

It would soon make "advanced compensation payments" to the passengers' nominated next-of-kin, "in order to meet their immediate economic needs", it added. The payments would not affect their rights to claim further compensation at a later stage, it said.

The families have been critical of the initial search process and the way they have been kept informed, with many accusing the Malaysian authorities of concealing information.

'Significant difficulty'

Late on Thursday, officials released the preliminary report on the missing airliner.

According to the draft, Vietnamese air traffic controllers contacted their counterparts in Kuala Lumpur at 01:38 to say MH370 was missing, 17 minutes after it disappeared off radar.

Media playback is unsupported on your device Media caption Flight MH370: Audio recording reveals final cockpit communications

The official search-and-rescue operation was launched four hours later, at 05:30.

The report also recommended the introduction of real-time tracking of commercial air transport.

The ministry's air accident investigation bureau said there had now been two occasions over the past five years when large passenger planes had gone missing and their last position was not accurately known - MH370 and Air France Flight 447 in 2009.

"This uncertainty resulted in significant difficulty in locating the aircraft in a timely manner," the report noted.

There is no requirement from the International Civil Aviation Authority (ICAO), the UN body that oversees global aviation, for real-time tracking.

Transport Minister Hishammuddin Hussein also released for the first time the recordings of conversations between MH370's pilots and air traffic controllers. A transcript was published earlier this month.

The plane's cargo manifest and seating plan was also published by Mr Hussein, along with a summary of events from the disappearance of the plane's radar blip until activation of the Rescue Co-ordination Centre.

Meanwhile, west of Perth an unmanned submarine is continuing to search an area of the ocean floor where acoustic signals consistent with a plane's flight recorder were detected earlier this month.

Australian Prime Minister Tony Abbott warned earlier this week that more specialist equipment had to be brought in to continue what could well be a very long, possibly fruitless operation.