Australian ships hunt for black box

More ships are joining the hunt for the missing Malaysia Airlines plane's black box as time ticks down on the device's tracker battery life.

Up to nine military planes, three civil planes and 14 ships will take part in Monday's search of an area spanning 234,000 square kilometres in the southern Indian Ocean.

The British Navy's HMS Echo is en route to assist the Chinese vessel Haixun 01, which has twice detected underwater pulse signals on a frequency used for the plane's flight data and cockpit voice recorders.

Australia's Ocean Shield, equipped with its own black box locator, is still investigating an "acoustic noise" detected about 300 nautical miles north of Haixun 01.

It is expected to join the Chinese ship when its investigation is completed.

It has been nearly a month since Flight MH370 from Kuala Lumpur to Beijing vanished on March 8 with 239 people on board, including six Australians and two New Zealanders.

Retired air chief marshal Angus Houston, who is co-ordinating the search, said the pulse signal detections were being taken "very seriously".

The Australian Transport Safety Bureau is working on refining the area where it is believed the aircraft crashed into the water.