INVESTIGATORS hunting the Malaysian passenger jet missing for more than four weeks believe a series of electronic pulse signals detected beneath the Indian Ocean may have come from the plane's black box.

Military and civilian planes, ships with deep-sea searching equipment and a British nuclear submarine were last night scouring a remote patch of the southern Indian Ocean off Australia's west coast after the apparent breakthrough by Chinese search teams.

The search has become increasingly urgent amid fears the black box will soon fall silent as its batteries die after sounding electronic "pings" for a month. Malaysia Airlines Flight MH370 is believed to have crashed in the area on April 9, after veering off course from its intended flightpath from Kuala Lumpur to Beijing.

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China's Xinhua News Agency reported a black-box detector (below) deployed by the ship Haixun 01 had picked up a signal at the frequency emitted by flight data recorders.

Xinhua also said a Chinese search plane spotted numerous white floating objects about 90 kilometres away.

Australian Air Chief Marshal Angus Houston said it was too early to say if there was a definite link to MH370 but Malaysian acting transport minister Hishammuddin Hussein said it was a positive development.