The head of the Australian-led search Angus Houston raised hopes Wednesday that wreckage will be found within days even as the black box batteries start to expire.
Houston's Joint Agency Coordination Centre (JACC) announced Thursday the search area off western Australia was now 57,923 square kilometres (22,364 square miles) - some 20,000 square kilometres down on Wednesday.
But Australian ship Ocean Shield is focused on an area of the Indian Ocean 2,280 kilometres (1,400 miles) northwest of Perth where it picked up two fresh signals Tuesday to match a pair of transmissions logged over the weekend as searchers try to pinpoint the exact crash zone.
No debris from the Boeing 777 which disappeared on March 8 has yet been found.
A large number of objects were spotted on the surface on Wednesday, JACC said, "but only a small number were able to be recovered.
"None of the recovered items were believed to be associated with MH370."
Officials had feared that the signals which were initially picked up might not be detected again, particularly since the batteries on the black box tracking beacons have a normal lifespan of about 30 days.
"Yesterday's signals will assist in better defining a reduced and much more manageable search area on the ocean floor," Houston told a press conference.
"I believe we are searching in the right area but we need to visually identify the aircraft before we can confirm with certainty that this is the final resting place of MH370."
Houston, however, again urged caution for the sake of the families of those aboard the flight, which mysteriously vanished en route from Kuala Lumpur to Beijing with 239 people on board, and said the search for more signals would go on.
"Hopefully with lots of transmissions we'll have a tight, small area and... in a matter of days we'll be able to find something on the bottom that might confirm that this is the last resting place of MH370," he said.
Australia confirmed Wednesday that the first signals were consistent with black box recorders.
"The analysis determines that a very stable distinct and clear signal was detected at 33.331 kHz and that it consistently pulsed at a 1.106 second interval," Houston said, explaining that the exact frequencies can vary according to time and conditions.
"They (experts) believe the signals to be consistent with the specification and description of a flight data recorder," he said.
No other ships will be allowed near the Ocean Shield, as its work must be done in an environment as free of noise as possible.
With the clock ticking on how long the black boxes could feasibly continue to transmit, Houston said it would not be long before a US-made autonomous underwater vehicle called a Bluefin 21 would be sent down to investigate.
"I don't think that time is very far away," he said.
Up to 10 military aircraft, four civil planes and 13 ships would take part in the search on Thursday, JACC said.
Fair visibility was predicted for the day with moderate southeasterly winds and isolated showers.
The case of the missing jet has baffled aviation experts and frustrated the families of those on board, two-thirds of whom were Chinese.
"I want to see the evidence that the plane is at the bottom of the sea," said Malaysian Tan Tuan Lay, whose daughter, 31-year-old bank employee Chew Kar Mooi, was one of the passengers on board.
"I am really sad (about) what has happened but I am prepared to accept whatever comes," Tan said when asked to comment on the fresh signals. - AFP