ST. CLOUD -- St. Cloud Fire Marshal Mike Post says an early morning apartment fire was arson.

The 100 unit apartment at 2015 27th Street Southeast had to be evacuated at about 1:45 a.m. after a mattress in a hallway caught fire. Post says the mattress had been in the hallway for several days and their investigation revealed it had been intentionally set on fire.

No one was hurt, but the damage is estimated at $70,000. Post says a single sprinkler head went off and put the fire out, but smoke and water damage affected 14 adjacent units.

Officials are offering a $2,500 reward for information in solving the crime. You can remain anonymous.

The arson hotline number is 1-800-723-2020.