A 72-year-old man is in custody after police said he threatened to "shoot the windows" of an elementary school in Duluth, Minnesota, on Thursday.

Police said they were alerted at about 6 p.m. to the threats involving Laura MacArthur Elementary School in the Denfield neighborhood.

Officers rushed to the suspect's home, located about a block north of the school, and arrested him.

A shotgun, an assault rifle and "various ammunition" were recovered during a search of his residence, police said, and he's expected to face charges for making threats of violence.

The threat comes more than two weeks after the deadly attack on students and parishioners during a back-to-school Mass at Annunciation Catholic Church in Minneapolis.

Hours after Thursday's arrest, schools in Princeton, Minnesota, were put on high alert after an apparent threat was made online. Classes commenced as scheduled, albeit with increased police and security presence.