The acoustic signals picked up by the Ocean Shield are in a different part of the Indian Ocean from those reportedly monitored by a Chinese ship last week.
"The audible signal sounds to me just like an emergency locator beacon," search coordinator Angus Houston said.
He described the finding as the "most promising lead so far" in the search for Malaysia Airlines flight MH370 that disappeared on a Kuala Lumpur to Beijing flight March 8 with 239 people on board.
The Ocean Shield, which is towing a pinger locator 3,000 metres below the surface, detected a signal for two hours and 20 minutes in its first run along a 3.2-kilometre course.
On its return run there was a second series of pulses consistent with both the flight recorder and the cockpit voice recorder that lasted for an unspecified period.
"We still have a lot of very painstaking work to do to confirm this is where the plane hit the water," he said. "This is a most promising lead (but) we haven't found the aircraft yet."Houston said finding wreckage was needed to confirm the location ofthe Boeing 777.
That might require the launching of an underwater craft."We need more evidence and the best evidence we can find is imagery from the autonomous vehicle that suggests the wreckage is on thebottom of the ocean and a photograph that demonstrates that and we could then say this is where the aircraft entered the water and the wreckage is on the floor of the ocean," the former armed forces chiefsaid.
The Ocean Shield will continue trawling in a box 4.8 kilometres square in the hope of re-establishing contact and getting a firm fixon the source of the acoustic signal.
"If they gain another acoustic event on that towed pinger locator, that will be the trigger to launch the autonomous underwater vehicle with the more accurate sonar and potentially camera for mapping andvisually looking at the ocean floor," Houston said.
"The focus is ontrying to re-acquire the acoustic signal they had 24 hours ago."