Officials said the AT&T building near 6th and Denver had smoke on several floors. No one was inside the building at the time and officials said the sprinkler system did activate, helping to contain the fire. Investigators believe the fire started in a cubicle on the third floor.
The building houses millions of dollars of telecommunications equipment for the entire region.
Detroit Ave. was shut down between 5th and 6th streets in front of the building while crews investigated.
Fire crews are still working to learn the cause of the fire and say no one will be allowed on the second and third floors of the building for remediation work.