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The vessel, Haixun 01, part of the multinational search effort, picked up a signal at 37.5Hz per second - meaning it could be the missing plane, China's official news agency Xinhua said.
"That is the standard beacon frequency" for both so-called black boxes - the cockpit voice recorder and flight data recorder, pinger manufacturer Dukane Seacom said early today. "They're identical."
The signal was detected around 25 degrees south latitude and 101 degrees east longitude.
The Australian-led joint agency coordinating the search for the missing Malaysian jetliner said the electronic signals were consistent with those of an aircraft black box.
However, the agency could not verify any connection between the signals and the missing Malaysia Airlines plane, Australian Air Chief Marshal Angus Houston told the Associated Press.
New Zealander Danica Weeks and her two young sons have been waiting a month for news of her husband Paul, who was on flight MH370 from Kuala Lumpur.
Early this morning (NZ time), at her home in Perth, Mrs Weeks was on the phone to friends and family trying to find out details.
A friend said she had been contacted by authorities.
"They have been in touch with her," she said. "She is aware of the fact that this is happening."
She will decide in the next two weeks when to return home to Christchurch to hold a memorial for her husband.
"I can't really leave here until such time as they find something," she told the Herald on Sunday a few hours earlier. "I would hate to be there and they find something and be so far away."
The Chinese report said it was not established whether the signal was related to the missing jet, and experts cautioned that no confirmation had been made that the signal was linked to the missing plane.
"This could be a variety of things," oceanographer Simon Boxall told CNN, saying the frequency was used by a variety of instruments.
"We've had a lot of red herrings, hyperbole on this whole search," said the University of Southampton lecturer.
"I'd really like to see this data confirmed. It could be a false signal."
But if this proves what investigators have been searching for, "then the possibility of recovering the plane - or at least the black boxes - goes from being one in a million to almost certain".
The announcement came nearly a month after the Malaysia Airlines flight disappeared, and on the same day the nation's acting transportation minister said three committees were being formed to tackle the disappearance of the flight.
It has been 31 days since Mrs Weeks kissed her husband goodbye.
She is now preparing to say a final farewell to the father of their two young sons, who was on the missing flight.
Mrs Weeks said she would hold a public memorial in Christchurch, and the airline would pay to fly her and sons Lincoln and Jack to the city.
Kiwi Paul Weeks, 38, an engineer living in Perth, and Aucklander Ximin Wang are among the 239 presumed dead after the flight bound for Beijing from Kuala Lumpur went missing on March 8.
In a cruel twist, the search for the missing plane is happening off the coast of their home.
"Paul always said if anything should happen to him, he would be taken back to Christchurch because that's his home," said Mrs Weeks.
On Friday, she met retired Australian defence chief Air Chief Marshal Angus Houston, who is leading the new joint agency co-ordination centre in Perth.
"From talking to them and going to the air base and seeing what was there and what's going on, if it's where they've calculated it to be, they will find it."
- By Amy Maas of the Herald on Sunday and Patrice Dougan of APNZ