As many as 10 people are believed to be trapped in the rubble of a building that collapsed Wednesday morning in Philadelphia, city Fire Commissioner Lloyd Ayers said, according to CNN affiliate WPVI.

The four-story building collapsed at the corner of 22nd and Market streets in Philadelphia's Center City area.

The fire department was called to the site at 10:43 a.m., Capt. Jeffrey Thompson told CNN. Thompson said it wasn't immediately clear whether it was an apartment building or an adjacent building scheduled for demolition.