Pierce County fire investigators continue to look into what sparked a blaze Thursday inside a closed-down feed mill in Midland.

Investigators have not been able to spend much time combing through the rubble inside the old Midland Feed Mill near Portland Avenue East because its not structurally sound,  Central Pierce Fire & Rescue spokesman Matt Holm said Friday.

The mill, which stopped operating in the mid-1990s, is a collapse hazard and will be demolished because of the damage done by Thursday morning’s fire.  Crews have closed 17th Avenue East between 97th and 99th streets East until the four-story structure is brought down.

The fire has not been ruled an arson. The Pierce County Fire Marshal’s Office has posted signs in the area, asking for information about what started the blaze, Holm said.

Meanwhile, the Northwest Insurance Council and Arson Alarm Foundation announced a reward of up to $10,000 for information that leads to an arrest of those responsible for setting the blaze.

In a press release, the non-profit organization noted the mill has been the target of vandals since it closed.

Anyone with information is asked to call the Arson Hotline at 800-55-ARSON (800-552-7766). Tipsters can remain anonymous.