Firefighters said flames at a vacant Dubuque Catholic school building appeared suspicious, in a Sunday evening news release.
The Dubuque Fire Department headed to Holy Ghost Elementary, 2901 Central Ave, around 6:30 p.m. for a report of smoke coming from the building.
When they arrived, firefighters found smoke on all three of the facility's floors.
"Fire was found on the first floor and extinguished," said an assistant fire chief in the release. "Additional companies were requested to rotate firefighters during the lengthy process of uncovering hot spots and opening confined areas that continued to burn."
The cause of the fire is under investigation.
Authorities said no one was hurt.
Central Ave was expected to be closed for several hours as firefighters finished their work.