The building collapsed before dawn after a severe thunderstorm. Officials said rescuers reported "hearing voices" in the rubble.
The nine-story building in Angeles city collapsed at around 3:00 a.m. local time (1900 GMT Saturday) after a severe thunderstorm.
There were no immediate reports of fatalities.
Some 26 people have been rescued, including two who were staying in an adjacent hotel that suffered damage.
Those individuals were in a "stable condition," city information officer Jay Pelayo said.
Many of those still unaccounted for are believed to be workers at the building site.
Authorities said rescue teams were "hearing voices" in the rubble.
"There are big chunks of concrete, and we need equipment to lift them up. That is what's challenging for the rescue right now," Pelayo said.
It was not immediately clear what caused the collapse.
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