The fire was reported just before 5 p.m. local time on Friday (21:00 GMT), and destroyed part of the R.M. Palmer Company chocolate factory in West Reading, Berks County.
Footage shared on social media captured the moment the explosion erupted at the site.
Additional video showed a massive plume of smoke emitting from the building as firefighters responded to the scene.
Citing West Reading police, local media reported that seven individuals were believed missing following the accident. At least six people were hospitalized with injuries.
A spokesperson for the Reading Hospital has indicated that eight people had been transported to the facility, specifying that two were considered in fair condition and that another was transferred. The remaining individuals were released without further issue.
The explosion at the chocolate factory is believed to have been likely caused by a gas leak.
An investigation is underway.