Undersea search for MH370 to expand: Australia

SYDNEY: Australia´s prime minister Monday announced an expanded search across a huge swathe of seabed where Flight MH370 might have crashed seven weeks ago, admitting it is now "highly unlikely" that any surface wreckage will be found.

A massive hunt for the Malaysian Airlines Boeing 777 in the southern Indian Ocean has so far yielded nothing on the surface or below, baffling authorities who are struggling to explain the loss of the aircraft.

"I regret to say that thus far, none of our efforts in the air, on the surface, or undersea have found any wreckage," Tony Abbott said.

"It is highly unlikely at this stage that we will find any aircraft debris on the ocean surface," he added, noting that a surface area of more than 4,500,000 square kilometres had been scanned.

"By this stage, 52 days into the search, most material would have become water logged and sunk."

Flight MH370 disappeared on March 8 carrying 239 people and is believed to have crashed in the southern Indian Ocean off west Australia after mysteriously diverting from its Kuala Lumpur to Beijing journey.

Abbott said the search would now enter a new phase that would involve undersea efforts being ramped up, with authorities scouring the ocean floor over an area of nearly 60,000 square kilometres.

"If necessary, of the entire probable impact zone which is roughly 700 kilometres by 80 kilometres," he said when asked when asked about the extent of the search area.

The search zone has been defined by analysis of satellite data, and was boosted by several detections of transmissions believed to have come from the plane´s black box recorders before their batteries died.

But a submersible Bluefin-21 scouring a 400-square kilometre zone centered around one of these transmissions has failed to yield results, prompting Abbott to announce an hugely expanded underwater search involving different technology, possibly a specialised side-scan sonar.