Police say multiple people, including an officer, have been shot at a high school in the east Tennessee city of Knoxville.
The Knoxville Police Department tweeted that authorities were on the scene of the shooting at Austin-East Magnet High School.
According to the Knoxville News Sentinel the shooter has been detained by police.
It remains unclear how many people have been shot and if school pupils were among those attacked.
The online posting said a Knoxville Police Department officer was reported among the victims.
Bob Thomas, the superintendent of Knox County Schools, tweeted that a shooting had occurred - but the building had been secured.
"The school building has been secured and students who were not involved in the incident have been released to their families," Mr Thomas said.
He added in a separate tweet that authorities were gathering information and about "this tragic situation", and that additional information would be provided later.
Police urged people to avoid the area. Details remained sketchy and news outlets showed numerous police and emergency vehicles at the scene.
The shooting comes four days after Tennessee Governor Bill Lee signed a bill into law which allowed permitless gun in the US state.