CONGERS- Investigators are looking into a fire in an unoccupied commercial building at 125 Wells Avenue in Congers on Wednesday.

The fire broke out just before 8 a.m. as heavy smoke poured out of the front entrance of the building.

Based on reported contents in the building, including food grade chemicals used in the production of vitamins and dietary supplements, the Rockland County HazMat team was called in to support the Congers Fire Department and several mutual aid departments.

During the firefighting operations, what authorities called a significant explosion occurred inside, resulting in a partial floor collapsing and increased smoke conditions.

No injuries were reported. At the time of the explosion, all firefighters had been evacuated from the building and attacked the blaze from a safe location.

As a precaution, Clarkstown Police evacuated about 200 residences and 12 commercial properties in the immediate area.

The police also coordinated with the Clarkstown Central School District as classes were in session.

The evacuation remained in effort for about an hour and 20 minutes and was lifted after air quality monitoring confirmed conditions were safe for return. Officials said at no time during the incident was air quality determined to be unsafe.