Military divers were trying to follow the pings to the boxes, believed to be on the floor of the Java Sea about 30 metres (100 feet) underwater, S.B Supriyadi, a director with the National Search and Rescue Agency told AFP.
The hunt came after the mangled tail of the Airbus jet was lifted from the sea on Saturday.
“The ping was detected about one kilometre (0.6 miles) east of the tail,” Supriyadi told AFP at the search headquarters of Panglakun Bun.
The Indonesian meteorological agency has said stormy weather likely caused the Airbus A320-200 to crash.
But a definitive answer is impossible without the black boxes, which should contain the pilots’ final words as well as various flight data.
Supriyadi and other officials involved in the search said they were confident the pings were from the black boxes, describing the signals as strong.
Supriyadi said an object believed to be the main body of the plane had also been detected close to the area from where the pings were emanating.
“We are now trying to check by sending our divers,” he added.
The search efforts, which have involved US, Chinese and other foreign naval ships, has recovered just 48 bodies.
Supriyadi said many of the bodies were believed to be trapped in the cabin, so reaching that part of the wreckage was also a top priority.
All but seven of those on board were Indonesian.
The non-Indonesians were three South Koreans, one Singaporean, one Malaysian, one Briton and a Frenchman — co-pilot Remi Plesel. (AFP)