MH370: Australia PM Abbott 'hopeful' about pulse signal
Australia has expressed hope that a pulse signal detected in the southern Indian Ocean could be linked to the missing Malaysia Airlines plane.
But Prime Minister Tony Abbott also warned this was "by no means certain".
Australian authorities are considering sending planes to the region where the signal was picked up by a Chinese ship.
A dozen military aircraft and 13 ships are searching three areas about 2,000 km (1,240 miles) north-west of the Australian city of Perth.
They will cover some 216,000 sq km on Sunday, the Australian agency co-ordinating the search says.
Flight MH370 disappeared en route from Kuala Lumpur to Beijing four weeks ago with 239 people on board.
The plane is believed to have crashed in the southern Indian Ocean, although no confirmed debris has been found.
Mr Abbott said he was "hopeful", but cautioned that this was "the most difficult search in human history".
"We are searching for an aircraft which is at the bottom of a very deep ocean and it's a very, very wide search area," he told reporters in Tokyo at the start of a trip to Japan, South Korea and China.
"While the best brains and the best technology in the world will be deployed, we need to be very careful about coming to hard and fast conclusions too soon."
On Saturday, Chinese vessel Haixun 01 picked up a so-called "ping" signal at about 25 degrees south latitude and 101 degrees east longitude, state-run Xinhua news agency said.
The signal reportedly had a frequency of 37.5kHz - the same as that emitted by the flight recorders.
Three people on board the boat were said to have heard the pings, which were not recorded as they came suddenly.
Xinhua also reported that a Chinese military plane had spotted a number of white floating objects about 90km away a few hours earlier.
Two Chinese naval ships were reported to have joined the Haixun 01 patrol ship in the search area.
"The characteristics [of the signal] reported are consistent with the aircraft black box," said retired Air Chief Marshal Angus Houston, the head of the Australian search operation, late on Saturday.
"However, there is no confirmation at this stage that the signals and the objects are related to the missing aircraft."
Australian naval vessel Ocean Shield is using a "towed pinger locator" from the US Navy, while the British HMS Echo, which has similar capabilities, is also searching for an underwater signal emitted by the data recorders.
The battery-powered signal fades after 30 days.
The area north-west of Perth has been picked on the basis of analysis of the satellite data.
Malaysia earlier announced it had set up three ministerial committees to help co-ordinate the search, and a new investigation team which would include members from Australia, China, the US, the UK and France.