WILMINGTON (CBS) — At least 150 firefighters are still mopping up hotspots after a stubborn fire broke out Monday morning at the ConocoPhillips refinery.

A 911 caller reported the fire, which broke out at 4:22 a.m. and severely damaged an administration building at 1660 West Anaheim Street.

The blaze destroyed the roof of the two-story building, which is primarily used by 100 employees of the engineering, finance and accounting departments of the nearby refinery.

No injuries were reported, but Anaheim Street is closed in both directions.