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Search co-ordinator retired air chief marshal Angus Houston told a press conference in Perth today that the information was encouraging.
He said the first signal was held for about five minutes and 32 seconds, while the second was held for about seven minutes.
"I believe we are searching in the right area," he said.
Two acoustic signals were detected over the weekend, it was revealed on Monday.
Mr Houston displayed a map that showed the first black box "pings", picked up on Saturday afternoon and evening, were near the final radar "handshake" the plane made with satellites.
The re-detections occurred on Tuesday afternoon and evening.
"We are looking for transmissions that are probably weaker than they would be earlier on," Mr Houston said.
It is 33 days since the plane went missing en route from Kuala Lumpur to Beijing - three days beyond the life of the black box beacon's battery.
But they are known to last several days longer.
Mr Houston said there were no plans to send more ships and pinger locators to the northern search area, which was being combed in tighter patterns, because it was crucial to keep the waters as quiet as possible.
Two thrusters were operating at the back of the Ocean Shield to propel it through the waves, but everything else had been turned off to optimise the operation of the pinger locator.
He said he was optimistic plane wreckage would be found "in the not too distant future".
But photographic evidence taken from a submersible would be required before the area was declared the final resting place of MH370.
"I'm not going to confirm anything until someone lays eyes on the wreckage," he said.
"We need to make hay while the sun shines. We need all the data we can," he said, referring to the weakening black box battery.
Mr Houston said the Chinese-led effort in the southern part of the search zone had not picked up any further audio signals since a detection was reported on Sunday.
He said he didn't believe it would be long before the automated underwater vessel was deployed because the last acoustic signal was very weak.
"I don't think that time is very far away."
The search continues for debris on the surface of the ocean, although none of the objects so far found has had any connection with MH370.
The Australian ship Ocean Shield is combing the northern part of the search zone in the Indian Ocean, more than 2000 kilometres northwest of Perth, while the Chinese ship Haixun 01 and British ship HMS Echo are operating at the southern end of the search area.