Australian Prime Minister Tony Abbott said Friday that he is confident the signals heard over the past days were from the black box of the missing Malaysian flight.

"We have very much narrowed down the search area and we are very confident that the signals that we are detecting are from the black box," Abbott told reporters in Shanghai, China.

"Nevertheless, we're getting into the stage where the signal from what we are very confident is the black box is starting to fade," he added. "We are hoping to get as much information as we can before the signal finally expires."

Australian navy ship Ocean Shield has detected suspicious signals for four times in the past week in a designated search zone in the Indian Ocean.

Addressing a luncheon event in the Chinese commercial center, Abbott later said searchers have known the approximate position of the black box.

"We are confident that we know the position of the black box flight recorder to within some kilometers," he said.

Meanwhile, the Australian prime minister cautioned that confidence in the approximate position is "not the same as recovering wreckage of almost 4.5 km beneath the sea and finally determining all that happened on that flight."

Noting that China was the first country to dispatch vessels once the search moved to the Indian Ocean, Abbott thanked the Chinese government and people for the help they've offered as Australia leads the search and recovery effort.

He said he is looking forward to providing Chinese President Xi Jinping with the latest update on the search operation when he meets Xi later Friday afternoon.

Voicing sympathy to the bereaved families of the 154 Chinese victims, Abbott said "Australia will not rest until we have done everything we could."

Separately, the Joint Agency Coordination Center (JACC) of Australia, which takes the lead in the international search effort, said in a statement that the signal picked up by an Australian surveillance plane was not related to the missing flight after analysis.

A Royal Australian Air Force (RAAF) AP-3C Orion aircraft detected a suspicious signal on Thursday in the vicinity of Ocean Shield.

"The Australian Joint Acoustic Analysis Center has analyzed the acoustic data and confirmed that the signal reported in the vicinity of the Australian Defence Vessel Ocean Shield is unlikely to be related to the aircraft black boxes," said JACC chief Angus Houston in a media release.

Houston, however, said there has been no major breakthrough in the search for the missing jetliner, based on the information currently available.

On the timing of the deployment of an autonomous underwater vehicle, Houston said that a decision will be made "on advice from experts on board the Ocean Shield and could be some days away."