CENTENNIAL, Colo. (KDVR) — A large commercial building fire sent plumes of smoke across the Denver metro area on Wednesday morning.

The amount of smoke lead to numerous 911 calls starting at 6 a.m. The fire was at a building near South Potomac Street, south of Arapahoe Road in Centennial.

Initially, crews were concerned the two-story commercial building was involved, however, they learned the fire was isolated to a separate generator building next door.

The building had a secure perimeter which presented a challenge for crews to attack the flames.

“[The] buildings are fortified to prevent criminals from getting inside and so firefighters have to have the tools to be able to break in and do what they need to do. So we did have to cut through a lot of gates, fences, locks, that kind of thing. That certainly delayed us getting to the building that was burning, but thankfully that’s an unoccupied building. There was nobody here,” said Eric Hurst with South Metro Fire Rescue. “This is a relatively isolated event. It’s just a widely visible.”

Hazardous materials created another hurdle for fire crews.

“The hazardous materials team will tell us exactly what’s inside and what that means how it could have been affected by fire, how it can be affected by water and perhaps if it’s in the water, what that might mean for the runoff? Where did the water go into the sewer system? And do we have to do anything about that? So lots of questions there,” said Eric Hurst.

The fire was put out by 8 a.m. and all hazardous materials concerns were mitigated, SMFR said.

No injuries were reported.

Here is a look at some of the different angles of the fire from SkyFOX:

The cause of the fire is under investigation.