Decatur firefighters responded to a fire at Del Carmen's Pizza at 22nd Street and Prairie Avenue Thursday morning.
Crews were called to the building at 6:49 and arrived to find smoke coming from the first and second floors, officials said. Once inside, they found heavy fire on the first floor and extending to the second floor and roof.
The building also housed three apartments, and firefighters said the occupants of those apartments made it out safely. They reported no injures.
The fire's cause was not immediately clear, Fire Chief Jeff Abbott said.
"The inspector's here. He's investigating to see what we can come up with," Abbott told reporters. "We believe it started on the first floor in a closet area, so we're going to narrow in our focus to that spot and then go from there."
Abbott said the building suffered significant smoke and water damage as well as damage to the roof. The roof was a metal deck roof, which was difficult for firefighters to get through, he said.