The fire killed at least 72 people when it ripped through a two-storey rubber slipper factory on Wednesday. Investigators believe sparks from welding equipment ignited nearby flammable chemicals, triggering a huge explosion.
Firefighters have spent Thursday pulling charred bones from the ruins. Police say charges will be brought against those responsible.
"Someone will definitely be charged because of the deaths. It doesn't matter if it's an accident, people died. Right now, we are investigating to clearly define what happened. For sure, someone will be charged," said national police chief Leonardo Espina.
Espina added that arson investigators were helping police in their inquiries.
Windows covered to prevent 'even cats from escaping'
The building was located in the rundown district of Valenzuela, on the northern edge of Manila, among a long line of factories. A relative of four people employed at the factory said windows were heavily reinforced.
Dionesio Candido, said iron grills and fencing wire covered windows on the second floor that "could prevent even cats from escaping."
Candido said he was allowed by authorities to enter the building, where he saw charred remains "piled on top of each other."
"When I saw them, [I felt] any parent or sibling would not be able to identify the victims," he told news agency Reuters.
Survivors say workers toiled for below the minimum wage, were not taught or made aware of safety standards, and had to work near foul-smelling chemicals. Some said they were only able to escape because they were near one of the building's few exits.
"I had never been involved in a fire drill ever," said Janet Victoriano, a five-year employee who said she left by the front door when the blaze started.
Fires are relatively common in the Philippines, where safety regulations are lax. Wednesday's incident showed the government was not doing enough, one analyst said.
"The factory fire is a blow to the [President Benigno] Aquino administration, which has prided itself on improving workplace conditions and prioritizing compliance with labor standards," said Eufracia Taylor, Asia analyst at global risk analytics firm Verisk Maplecroft.
jr/msh (Reuters, AFP)