Hunt for Malaysian plane heads underwater to find black box

The search for missing Malaysia Airlines Flight MH370 in remote seas off Australia headed underwater on Friday, with a U.S. Navy high tech "black box" locator deployed for the first time as the battery life of the cockpit data recorder dwindles.

Australian authorities said the so-called Towed Pinger Locator will be pulled behind navy ship HMAS Ocean Shield, searching a converging course on a 240 km (150 miles) track with British hydrographic survey ship HMS Echo.

"The area of highest probability as to where the aircraft might have entered the water is the area where the underwater search will commence," Retired Air Chief Marshal Angus Houston, the head of the Australian agency coordinating the operation, told reporters in Perth.

"On best advice the locator beacon will last about a month before it ceases its transmissions so we're now getting pretty close to the time when it might expire."

On Monday it will be 30 days since the jetliner lost communications and disappeared from civilian radar less than an hour into an overnight flight from Kuala Lumpur to Beijing on March 8.