ST. LOUIS — A firefighter was treated for dehydration while fighting a fire in north St. Louis early Friday morning.

Just after 3 a.m., the St. Louis Fire Department responded to the 8700 block of Riverview Boulevard for reports of a fire at a two-story multi-use commercial building. There, firefighters found heavy fire and smoke coming out of the second floor, which quickly spread to the roof.

The fire was soon upgraded to a second-alarm fire. One of the responding firefighters was treated then released for dehydration while on the scene.

St. Louis Fire Chief Dennis Jenkerson deemed the fire "very suspicious," adding that multiple fires were set throughout the building.

The fire remains under investigation.