Missing Malaysia Airlines flight MH370: Black box has fallen silent, admits Australian Prime Minister Tony Abbott

Batteries of the flight’s black boxes have most likely died, leaving a 500 square mile area to be searched by a slow moving robotic submersible

A Buddist devotee offers prayers for the missing Malaysian Airline plane MH370 in Bentong, Pahang, Malaysia (EPA)

Australian Prime Minister Tony Abbott is warning that the search for the missing Malaysia Airlines flight is likely to be long after pings believed to be from locator beacons on the all-important black boxes fell silent, meaning the batteries have most probably died.

The last of four strong signals coming from 4,500 meters (15,000 feet) below the surface were heard on the 8 April. The batteries on the black boxes, which record flight data including conversations from the cockpit, only last a month, meaning the window has passed.

The pings already captured have however allowed the search area to be narrowed down to a 500-square-mile patch of the seabed - about the size of Los Angeles. Once officials are confident no more sounds will be heard, and the search area can be narrowed no further, a robotic submersible will be sent down to slowly scour for wreckage across the vast area.

The Bluefin 21 submersible will take six times longer to cover the same area as the ping locator, and will need about six weeks to two months to canvass the current underwater zone.

“No one should underestimate the difficulties of the task still ahead of us,” Mr Abbott said in Beijing on Saturday, the last day of his China trip.

“There's still a lot more work to be done and I don't want anyone to think that we are certain of success, or that success, should it come, is going to happen in the next week or even month. There's a lot of difficulty and a lot of uncertainty left in this,” he added.

Mr Abbott had met with Chinese President Xi Jinping a day earlier to brief him on the search for the plane, which was carrying 239 people - most of them Chinese - when it disappeared on 8 March en route from Kuala Lumpur to Beijing.

After analyzing satellite data, officials believe the plane flew off course for an unknown reason and went down in the southern Indian Ocean off Australia's west coast.

Malaysian, Defense Minister Hishammuddin Hussein on Saturday refuted a front-page report in a local newspaper that the flight’s co-pilot tried to make a mid-flight phone call shortly before the plane disappeared.

Mr Hishammuddin, who is also the acting transport minister, said that if this were true, he would have been made aware of the phone call much earlier, but was not.

Australian Maritime Safety Authority image showing the current planned search area in the Indian Ocean for the flight MH370 on 13 April 2014 (EPA)

“I cannot comment (on the newspaper report) because if it is true, we would have known about it much earlier,” Hishammuddin said, adding that it was irresponsible for anyone to take the opportunity to make “baseless” reports.

The surface area being searched for floating debris on Sunday was 22,203 square miles of ocean extending about 1,367 miles northwest of Perth. Up to 12 planes and 14 ships were participating in the hunt.