(CNN)At least 67 people were killed after a fire engulfed a footwear factory in the northern Philippines, authorities said Thursday.
The blaze swept through a slipper and shoe factory in Valenzuela City on Wednesday, Mayor Rex Gatchalian told reporters at a news conference.
Retrieval operations are still underway at the site, and fire officials have said they expect to find more bodies when they reach the building's second floor, which they have warned could collapse.
Five people pulled alive from the burning factory on Wednesday were taken to local hospitals. Authorities said late Wednesday that the total number of survivors was still unclear.
The blaze started before noon Wednesday, and fire officials declared it under control by late afternoon, authorities said.
The city government said the fire was believed to have been caused by sparks from welding work on the factory's gate setting alight chemicals in nearby containers.
The flames spread in seconds, witnesses said.
"We tried to put the fire out by pouring water and using the fire extinguisher but it was difficult already," Steve Chua, a worker in the factory, told police, according to CNN Philippines.
Thick black smoke from the highly combustible materials made it hard for the firefighters to put out the fire and look for survivors.
Gatchalian said the facility was owned by the Kentex Manufacturing Corp.
Valenzuela City is part of the densely populated metropolitan region around the Philippine capital, Manila.