Flight QZ8501 lost contact with air traffic control in bad weather on Dec. 28, less than halfway into a two-hour flight from Indonesia's second-biggest city of Surabaya to Singapore.

“At 7:11, we succeeded in lifting the part of the black box known as the flight data recorder,” The Hindu reported quoting Fransiskus Bambang Soelistyo, the head of the National Search and Rescue Agency, told reporters at a news conference.

The second black box with the cockpit voice recorder has been located, based on pings from its emergency transmitter, but not yet retrieved, Madjono Siswosuwarno, the main investigator at the National Transportation Safety Committee, told Reuters.

Officials hope the black boxes, found near the wrecked wing of the plane, will reveal the cause of the crash. The national weather bureau has said seasonal storms were likely a factor.

The recorders are expected to be taken to the capital, Jakarta, for analysis and it could take up to a month to get a complete reading of the data. Officials did not provide details of the condition of the black boxes.

“The download is easy, probably one day. But the reading is more difficult ... could take two weeks to one month,” Mr. Siswosuwarno said.

Forty-eight bodies have been retrieved from the Java Sea and searchers believe more will be found in the plane's fuselage.  Relatives of the victims have urged authorities to make finding the remains of their loved ones the priority.