Arson was blamed for a blaze still burning over the weekend in Arden Hills, the Lake Johanna Fire Department said on social media.

The fire began Saturday and engulfed two buildings south of County Road I and Fairview Avenue, sending plumes of black smoke into the sky.

Authorities were allowing the blaze to "burn itself out" over the next few days. They advised residents to call 911 if the flames spread beyond the structures.

The buildings were part of the sprawling Twin Cities Army Ammunition Plant built in the 1940s. Made of creosote timbers, they were used to store ammunition during World War II.

"This will continue to smolder, and we will monitor the situation," the Fire Department said on Facebook.

It said smoke and possibly flames will continue to be visible.