The fire was reported around 1:15 a.m. at the Carriage House near the Carriage House Apartments and the Colonade Manor Apartments in the 100 block of Washington Lane.
The flames were contained to the Carriage House, which was used as an office and a storage facility.
Witness Leslie Nettles watched as the fire erupted through the roof.
"It looked like it was just going to actually collapse totally in because the fire came through the roof," Nettles said. "The smoke covered and you couldn't see nothing."
There were no further details on the cause of the fire.
However, according to residents, a threat toward one of the building's staff was spray-painted on the building in recent weeks.
Authorities have not said if that vandalism was connected to the fire.
There were no evacuations from the apartments, though residents were told to remain in place.
The fire was brought under control about two hours later.
"The nature of the construction of the building and its age were the biggest factors that made it difficult to fight the fire," said Chief Chris Bors of the McKinley Fire Co.
A firefighter sustained minor injuries battling the blaze.
The Carriage House was the original building on the property before the adjacent high-rises were built.
In a statement, a spokesman for Colonade said:
"We are fully cooperating with all public safety personnel during their investigation, and will be unable to speculate or comment about the situation during that process. We are grateful to the brave firefighters for all of their efforts in battling the fire and are thankful that none of our residents or employees were endangered."