One person has been killed in the shooting, Local 10 News reports, citing a police statement.
"Multiple gunshot victims reported, including a KPD officer. The investigation remains active at this time," Knoxville police said on Twitter.
Authorities did not say if the gunman had been taken into custody but the Knoxville News-Sentinel reported that one person had been detained in connection with the shooting.
Television news images showed police and fire crews surrounding Austin-East High School in east Knoxville.