Firefighters try to control a raging fire at a factory in Valenzuela City, north of Manila May 13, 2015.[Photo/Agencies]

The incident showed President Benigno Aquino's government in poor light, said Eufracia Taylor, an analyst at global risk analytics firm Verisk Maplecroft.

"The factory fire is a blow to the Aquino administration, which has prided itself on improving workplace conditions and prioritising compliance with labour standards," Taylor said.

Factory owner Veato Ang said about 200 to 300 people worked in the factory, which made flip-flops and slippers for Kentex Manufacturing Inc.

Identifying the charred remains of victims will be a difficult task, said Dionesio Candido, whose 19-year-old daughter was among the factory workers.

"I entered the building because I thought I might still be able to identify the remains," said Candido, 62.

But he saw four piles of charred bones and skulls, with the victims appearing to be hugging each other.

"When I saw them, (I felt) any parent or sibling would not be able to identify the victims," Candido added.