NIAGARA, Wis. - A man wearing camouflage clothing and carrying an assault rifle walked out of the woods and shot four young people who had gathered at a Wisconsin river to go swimming, killing three of them and wounding one.

More than 100 law enforcement officers from at least 10 agencies searched Friday for the gunman, a middle-age man who was last seen near the town of Niagara, across the state line from Michigan's Upper Peninsula.

Officers set up roadblocks and evacuated an unknown number of homes.

Chief Deputy Jerry Sauve of the Marinette County Sheriff's Department said his office got a call around 6 p.m. Thursday reporting a shooting in the town of Niagara along the Menominee River.

A command post was set up for state and other law enforcement personnel being brought in to help sheriff's officials investigate what Sauve called an "active shooter situation."

The victims had gathered near a railroad bridge on the Menominee River when the gunman came out of the woods and opened fire about 5:30 p.m. Thursday, according to Sheriff Mike Kanikula.

Two of the bodies had not been removed from the scene Friday because of a fear that the shooter was still in the area, the sheriff said.

The dead were identified as Tiffany Pohlson, 17; Anthony Spigarelli, 18; and Bryan Mort, 19. A fourth victim, 20-year-old Daniel Louis Gordon, was wounded.

Niagara is about 210 miles north of Milwaukee.