SHERBROOKE, Quebec (AP) — An explosion and fire at a manufacturing plant outside Montreal injured four people Thursday, police said.

The blast at the Sherbrooke, Quebec facility led to the fire, which produced clouds of smoke that authorities feared was toxic, said police spokesman Rene Dubreuil.

Dubreuil said four people are seriously injured. It was unclear if their injuries are life-threatening.

The plant belonging to Neptune Technologies & Bioressources produces and exports health products.

Environment Quebec said the toxicity concern stemmed from the plant's acetone reserves, which were struck by the fire. Acetone is flammable and, when ingested, can cause irritation.

However, officials said they were more concerned about the possibility of soil or water contamination than the risk associated with breathing the air near the blast site.

Police said it's unclear what caused the blast. Thick black plumes were seen rising from the facility.

Employees were evacuated from the plant within minutes, and supervisors performed a head count outdoors.