ALL hostages have been released from a high school classroom where an armed student had been holding 23 students and a teacher in Wisconsin, police say.

Local police chief Jeffrey Skorik said hostage negotiators were inside Marinette High School, Fox News reported on its Green Bay news website about 8pm local time (1pm today AEDT).

He said all contact had been through the teacher in the classroom.

Chief Skorik said there had not been any threats or demands made at this point.

Earlier, he said the male student was armed with a gun, but there had been no reports of injuries.

Marinette County emergency management director Eric Burmeister said a high school administrator called authorities after 3pm local time (8am today) to say an armed student had burst into a classroom.