An Australian vessel heard the signals again on Tuesday afternoon and evening, the search chief said.

Signals heard earlier have also been further analyzed by experts who concluded they were from "specific electronic equipment", he said.

Flight MH370 disappeared on 8 March, carrying 239 people.

It was travelling from Kuala Lumpur to Beijing when it lost contact with air traffic controllers.

Malaysian officials say that based on satellite date, they believe it ended its flight in the southern Indian Ocean, thousands of kilometers from its intended flight path.

The Australian vessel, Ocean Shield, has been towing a pinger locator to listen for signals from the plane's flight recorders in waters west of the Australian city of Perth.

On Tuesday, it located the signals again, the first time for five minutes and 32 seconds, and the second time for around seven minutes, said Air Chief Marshall Angus Houston, who heads the joint agency coordinating the search.

"Ocean Shield has now detected four transmissions in the same broad area," he said. "Yesterday's signals will assist in better defining a reduced and much more manageable search area on the ocean floor.

"I believe we are searching in the right area but we need to visually identify aircraft wreckage before we can confirm with certainty that this is the final resting place of MH370."

Work would continue to refine the search area before a submersible could be sent down, he said.

Experts at the Australian Joint Acoustic Analysis Centre had also analysed the first two signals heard over the weekend, he added.

Their analysis showed that a "stable, distinct and clear signal" was detected. Experts had therefore assessed that it was not of natural origin and was likely from specific electronic equipment.

"They believe the signals to be consistent with the specification and description of a flight data recorder," ACM Houston said.

BA/BA