Military chief Hadi Tjahjanto said specialist navy equipment will be deployed to reach the victims who are believed to be trapped inside the sunken ferry.
"Our navy equipment that can reach up to a depth of 600 meters will be able to determine the exact location of the ship," he said.
"When we can determine where the ship is, we will determine the technique of how to retrieve the victims."
Member of an Indonesian search and rescue team prepare their dive gear as they search for victims. Source: AAP
Bad weather has complicated efforts to locate the sunken vessel.
Divers have only been able to reach depths of 50 metres, while an underwater drone used in the search has a maximum operating depth of 200 metres.
Only 18 survivors, including the captain, have been found from the 184 people on board, all within several hours of the accident.
Muhammad Syaugi, head of the national search and rescue agency, revised down the figure of those missing from 192 to 184. He said the earlier higher figure had double counted some victims.
Authorities say the search will continue for another four days until Sunday, seven days after the incident.
Police warn of criminal investigation
Indonesian authorities have warned a criminal investigation could be launched into the ferry sinking.
Indonesian police have questioned the captain of a ferry that sank without trace in a volcanic lake in Sumatra, warning that a criminal investigation could be launched over the disaster that has left at least 192 people missing.
Desperate relatives awaiting news of loved ones prayed and sang hymns at the port on Lake Toba after one of Indonesia's worst ferry disasters in years.
elatives of the victims on the sunken ferry KM Sinar Bangun sit and wait for news at Tigaras port. Source: AAP
"We see there's a possibility to begin a criminal investigation because of negligence that resulted in people losing their lives," national police chief Tito Karnavian said during a visit to the base of rescue operations at the lake, one of the world's deepest.
"The captain may be named a suspect," Karnavian said, adding that regional transport officials would also be questioned about supervision.
Ferry captain questioned
Authorities were trying to get clearer information from the captain and survivors on where the vessel went down.
"(The captain's) health remains unstable. We asked him some questions, but he has yet to remember clearly," police official Agus Darojat told Metro TV.
Waiting at the quayside for news of the family of her 20-year-old daughter who took the ill-fated ferry, one distraught mother criticised the disorganised nature of the initial rescue effort.
"Just looking at the videos of them throwing lifesavers, it looked haphazard," the woman, Turia, said, describing attempts by nearby ships to help survivors.
President Joko Widodo said the government would push to prevent future boat accidents.
"I ask that this kind of case will not happen again and I have asked the transport minister to evaluate all safety standards for ferry transport," he said in a statement.
- with AP
