March 25 (UPI) — At least two people were killed and nine others were declared missing following a powerful explosion that rocked a chocolate factory northwest of Philadelphia, authorities said Saturday.

Police in West Reading Borough, Pa., told reporters several other people were injured by the explosion at the R.M. Palmer Co. plant, located about 60 miles northwest of Philadelphia in Bucks County.

The explosion happened just before 5 p.m. on Friday, shaking the surrounding neighborhood while leveling at least one building and causing what appeared to be extensive damage to a nearby structure.

Traffic camera footage showed massive flames and thick plumes of black smoke rising into the air at the scene of the explosion.

Tower Health spokeswoman Jessica Bezler told WGAL-TV eight injured people were taken to Reading Hospital.

The cause of the explosion remains under investigation.

“The tragic explosion at R.M. Palmer Company and loss of life has shaken our community,” West Reading Borough Mayor Samantha Kaag said in an issued statement. “It is always difficult to come to terms with such sudden and unexpected events and unfortunately that is what has happened today. Our deepest sympathies are with the families and friends of those who have been affected.”

This is a developing story. Please check back for updates.