Gatchalian said at least 30 people had been injured and expressed hope that some of the missing may have escaped.
"The city government is still praying and hoping that the 26, some of them, must have gotten out earlier in the morning and had gone to relatives and have not logged on at city hall. So we are still hoping that the number 26 will still go down," he said.
Dionesio Candido, whose daughter, granddaughter, sister-in-law and niece were among the missnig, told The Associated Press iron grills reinforced with fencing wire covered windows on the second floor that "could prevent even cats from escaping."
Candido said he was allowed to re-enter the bulding, where he saw charred remains "piled on top of each other" but could not say how many.
District Fire Marshal Wilberto Rico Neil Kwan Tiu said he was among the first to reach the second floor of the building after the fire and saw "numerous bodies" but could not specify how many.
Local media reports quoted relatives as saying their kin sent text messages saying they were on the second floor, but contact was lost shortly after.
Gatchalian said the fire was apparently ignited by sparks from welding work being done at the factory`s main entrance door, triggering an explosion of the chemicals used to make the slippers.
Workers fled to the second floor where they were trapped, he said. He was unsure if there were any fire escapes there.
Tiu, the fire marshal, said the building had other exits but apparently the workers were overwhelmed by the thick black smoke from the burning rubber and chemicals, which are highly flammable and caused the blaze to spread quickly.
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