Story highlights Many of the dead were found on the second floor of the factory

Officials say they believe sparks from welding may have set off the blaze

(CNN) A fire that engulfed a footwear factory in a suburb of the Philippine capital has killed 72 people, authorities said Thursday.

The blaze swept through the slipper and shoe factory in Valenzuela City on Wednesday, sending huge clouds of thick black smoke billowing into the sky.

Investigators were still pulling bodies from the charred ruins a day later.

Many of the dead were recovered from the second floor of the building, authorities said, suggesting people had become trapped there.

It wasn't clear Thursday whether fire officials expected to find any more bodies in the burnt-out shell of the factory, which was owned by the Kentex Manufacturing Corp.

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