Search and rescue agency chief Bambang Soelistyo said as of Friday morning 103 passengers aboard the ill-fated boat had been recovered, with just 40 found alive.
“If the information is correct, we are still searching for 15 other missing people,” Soelistyo told AFP, adding that all the bodies found so far were within the search area.
The ferry operator said the boat was carrying 116 people when it ran into trouble, but Soelistyo said there were two canteen staff who were not mentioned on the manifest.
Ten vessels — including navy warships — and two aircraft are scouring the seas for any sign of the missing, while families wait anxiously for news in Siwa, the port town where the stricken vessel was heading.
Soelistyo said according to the initial plan the search should end on Saturday but could be extended depending on a final evaluation of the operation.
The ferry sank on rough seas last Saturday with survivors describing massive waves smashing into the vessel before the engine died and the order was made to abandon ship.
The Indonesian archipelago of more than 17,000 islands is heavily dependent on ferry services but fatal accidents are common.