A Chinese ship twice detected a "pulse signal" at a frequency used by aircraft black boxes, while an Australian vessel is investigating a separate "acoustic noise" in the search for flight MH370.
Retired Air Chief Marshal Angus Houston, who is co-ordinating the search, told reporters in Perth on Sunday the Chinese ship Haixun 01 had detected two "acoustic events" which provided "some promise" and required a full investigation.
The first signal was detected on Friday and the second, which lasted 90 seconds, was detected on Saturday within two kilometres of the original detection.
"This is an important and encouraging lead but one which I urge you to continue to treat carefully," Air Chief Marshal Houston said.
He warned no signals or objects found in the ocean had been verified as being from the missing Malaysia Airlines plane.
British naval ship HMS Echo would take about 14 hours to reach the search zone, he said.
Australian naval vessel Ocean Shield is looking at another "acoustic noise" in a separate area and will go to the zone when that task is completed.
Air Chief Marshal Houston said he only learned about Ocean Shield's detection on Sunday morning and it could be a couple of days until the search was resolved.
"We will pursue these leads to their conclusion," he said.
Air Chief Marshal Houston said there had been "fleeting acoustic events" rather than a continuous transmission.
"If you get close to the device, we should be receiving it for a longer period of time than just a fleeting encounter," he said.
"But we've got a transmission (so) we must investigate it."
An observer looks out a window onboard a RNZAF P3 Orion during the search operations for missing Malaysia Airlines Flight MH370
Corrected satellite data indicated the ill-fated Malaysia Airlines plane might also have been travelling faster, which meant the search was moving further south - to about where Haixun 01 was - but was still within the same search zone, Air Chief Marshal Houston said.
He added that it was a "painstaking process" and there had been few leads so far that had narrowed down the search area, warning there could be similar unverified leads over the coming months.
Air Chief Marshal Houston said because the Chinese search area was 4.5km deep, any recovery operation would be demanding and take a long time.
But he stressed that authorities would first have to establish that there was actually something there.
"We're a long way from making that conclusion," he said.
It is now day 30 of the search and near the end of the black box emergency beacon's battery life.
While the battery could last an extra eight to 10 days beyond that, Air Chief Marshal Houston admitted they were running out of time.
He also defended Australia's relationship with China, saying he became aware of the first Chinese signal detection quickly because there was a journalist on board but was also informed by the Chinese government about the same time.
He said he learned about the second ping "quite some time ago" and was "very satisfied" with the level of communication from the Chinese.
The Boeing 777 was carrying 239 passengers when it vanished on March 8 en route from Kuala Lumpur to Beijing, triggering an international search that started in the South China Sea before shifting to the Indian Ocean.
Up to 10 military planes, two civilian aircraft and 13 ships are assisting in Sunday's search for the missing plane, about 2000km northwest of Perth, totalling about 216,000 sq km.
SGT Sean Donaldson prepares to deploy a smoke marker onboard a RNZAF P3 Orion during search operations.