Speaking to reporters in Canberra on Monday, Australian Prime Minister Tony Abbott announced an expansion of search efforts to locate Malaysian Airlines flight MH370. However, the latest phase would discontinue the use of aircraft to locate wreckage.

"It is now 52 days since Malaysia Airlines flight MH370 disappeared and I'm here to inform you that the search will be entering a new phase," Abbott said.

"I am now required to say to you that it is highly unlikely at this stage that we will find any aircraft debris on the ocean surface," he added.

The Australian premier, whose country is leading the multinational search, also cited safety issues for aircraft crews involved in the hunt for the missing Boeing 777.

"With the distances involved, all of the aircraft are operating at close to the limit of sensible and safe operation," he said.

Instead navy resources would be implemented underwater to investigate the zone which investigators have identified as the possible crash area based on satellite data.

The U.S. Navy's Bluefin-21 mini-submarine would be part of the new mission. It has already scoured an area of 400 square kilometers (154 square miles) and 4,500 meters (15,000 feet) deep based on transmissions believed to have been emitted from the passenger jet's blackbox.

"If necessary [the new phase will include] the entire probable impact zone, which is roughly 700 kilometers by 80 kilometers," Abbott said, adding that the remainder of the search would be conducted as "humanely as possible."

Malaysian Airlines flight MH370 disappeared on March 8 during a flight from Kuala Lumpur to Beijing. According to satellite data, the aircraft - which had 239 people on board - flew off course and likely crashed into the southern Indian Ocean, off of the southwest coast of Australia.

kms/jr (AP, AFP, dpa)