An 18-year-old in Wisconsin who shot two students outside of their high school prom has been pronounced dead, according to authorities.

Jakob Wagner “showed up” to the dance in the town of Antigo about 11pm on Saturday evening and started firing his rifle outside the building.

He shot two students as they exited the building, one of whom was critically injured and the other received minor injuries, said Lieutenant Jamie Lenzer of the Antigo Fire Department.

As police patrolled the carpark they shot Mr Wagner, a former student at the school. He was taken to hospital and died at 1am Sunday morning.

“Officers were in the parking lot patrolling the activities and heard the shots, and an officer immediately fired upon the shooter, stopping the threat,” said Eric Roller, Antigo's police chief, in a statement.

“All the people within the prom were eventually escorted from the school and are safe.”

Police have not commented on a possible motive for the shooter.

Sonia Reed, whose son Matthew attended the prom, told news channel WSAW that she was on campus earlier that evening for the “grand march,” where students and their dates form a procession and parents cheer them on before the school announces the prom queen and king.

She estimated there were between 100 and 120 students at the dance.

“I have two other children that's in the high school, and they don't want to go back, period,” Ms Reed said. “They're just beyond freaking out here.”

Antigo is a small town of about 8,500 residents. Ms Reed described Antigo as a farmtown where students participate in the annual “Drive Your Tractor to School” day.