The search for wreckage of Malaysia Airlines Flight 370 will soon enter a new phase, when two sophisticated tracking devices arrive from the United States to help detect the aircraft's black box.

Pentagon press secretary Navy Rear Admiral John Kirby said on Monday a towed pinger locator and a Bluefin-21 robotic underwater vehicle have already left New York for Western Australia. The equipment should arrive in the next day or two.

A US Navy black box locator is loaded on to a plane. Credit:US Navy

The pinger uses acoustic signals to track down the black box flight recorder, to a maximum depth of 6000 metres.

The Bluefin is an unmanned device with sophisticated sonars that can scan the ocean's depths to detect underwater wreckage. It can produce high-resolution imagery of the ocean floor at a depth of up to 4500 metres and operate for up to 25 hours, according to the Pentagon.