The blaze at House Technology Industries was under control but had not been fully extinguished nearly 24 hours after it started in General Trias in Cavite province, south of capital Manila, governor Jesus Crispin Remulla said.
Firefighters hoped to enter and inspect the gutted factory, which occupies 15 acres of land, on Thursday.
About four of the injured remain in a critical condition, Mr Remulla said, adding that some employees jumped from windows to escape the blaze at the three-storey building, where pre-fabricated house parts are manufactured for export to Japan.
"We can't conclude anything as long as the fire is
still there and we have not seen any casualties," Mr Remulla said on the possibility of workers being trapped in the overnight inferno.
The fire apparently started when a machine malfunctioned and triggered small explosions in a section with combustible materials as two shifts of workers of about 3,500 each were changing places, he said.
Massive amounts of black smoke billowed in the night sky as red flames raged through the factory, which employs about 15,000 workers and is the largest in Cavite province, he said.
Company officials were doing a count to find out if any more people were missing at the factory.