The plane’s black boxes should help explain why the almost-new Boeing 737 MAX 8 jet went down in waters about 35 metres (115 ft) deep just off Jakarta, the capital.
A “ping” sound believed to be emitted by one of the black boxes had been getting clearer, Haryo Satmiko, deputy chief of the national transport safety panel, told Reuters earlier on Thursday.
An underwater drone had detected an object suspected to be part of the fuselage, he added.
A team of divers had gone down since 5 a.m. to map the area where the black box is thought to be, Haryo said, describing sea conditions as normal.
Strong currents on Tuesday hampered the search, with the effort further complicated by the presence of energy pipelines nearby.
However, officials had said they were confident they were searching in the right area, having found items, such as life jackets, trousers and magazines, thought to be from the plane.
If found, the fuselage would be lifted using a crane, because of the many bodies likely to be trapped inside, Muhammad Syaugi, the chief of Indonesia’s search and rescue agency, said on Tuesday.