A 52-year-old pilot from Hermantown, Minn., was killed Friday in a plane crash near Grassy Point in Duluth, the St. Louis County Sheriff's Office said.

He was identified as David Rathbun and was alone on the plane, the Sheriff's Office said.

Several 911 callers reported the crash just after 4 p.m. on the harbor ice near Bong Bridge behind the former Lake Superior Paper mill, the Sheriff's Office said.

Sheriff Gordon Ramsay said in a tweet that the plane was a smaller model and partially submerged. No further description of the aircraft was released.

"First responders were unable to save the sole occupant of the plane, and our heartfelt sympathy is with friends and family of the pilot tonight," Ramsay said.

The Federal Aviation Administration, National Transportation Safety Board and Midwest Medical Examiner's Office were investigating, the Sheriff's Office said.

Other agencies responding to the crash included Duluth police and fire departments, the county rescue squad, the U.S. Coast Guard and the Douglas County, Wis., Sheriff's Office. Nothing else in the area of the crash was damaged, the Sheriff's Office said.