Some remains were found clustered together in parts of the vessel, forensic specialist Richard Allan Mangalip from the Philippine National Police said on Sunday, while others were scattered across different areas of the ship, which was carrying more than 130 people and was nearing its destination when it caught fire.
The ferry was heading southwest from Manila to Coron, in Palawan province, a trip that generally takes about 20 hours.
"Most of them are already in a charred condition," Mangalip told reporters, adding authorities could not provide a firm timeline for identification because of the volume of specimens that must be examined.
"It could be weeks, or it could be much longer."
That assessment came a day after rescuers recovered 41 additional remains from the ferry, raising the death toll to 76 and leaving 13 people unaccounted for.
Officials said more remains could still be found because investigators have not yet fully searched flooded sections of the vessel.
Firefighters entered the ferry for the first time on Friday after extinguishing the blaze more than a day after it broke out.
Images released by the coast guard showed the scale of the destruction inside the vessel, with rows of steel bed frames twisted by intense heat and covered in ash.
Investigators said they had yet to determine where the fire started and were still trying to access key sections of the vessel, including flooded lower decks and the engine room, where evidence could help establish the cause.
A statement from the Maritime Industry Authority, citing survivor accounts, said two explosions were heard inside the vessel shortly before the fire broke out.
A representative of shipowner Atienza Inter-Island Ferries said at the same press conference the company was co-operating fully with investigators and would continue assisting affected families.
The fire is the latest in a string of deadly maritime accidents in the Philippines, an archipelago of more than 7600 islands where millions rely on ferries and small boats to travel.
