The vacant Marktplatz Mall in New Ulm, Minn., caught on fire in Wednesday's early morning hours.

The entire roof of the mall was billowing smoke when firefighters arrived at 4:21 a.m., New Ulm Assistant Fire Chief Aaron Wilfahrt said Thursday.

Clothing, couches, chairs and household items were burning inside the mall, which has sat empty for six years, he said.

The blaze was difficult to fight as first responders did not know where it started, but crews from New Ulm, Sleepy Eye and Courtland helped get the flames under control within an hour and a half, Wilfahrt said.

The fire remained largely confined to the roof and did not spread into the structure, he said. There were no injuries.

The cause of the fire is still under investigation, he added.

Marktplatz Mall has been closed as a retail space since 2018, and it formerly housed a Herberger's store, the New Ulm Journal reported.