The gunman, who was identified as a student at the school, died at the scene, TBI said. Authorities said they are not releasing the student's name at this time.

Willson was hit at least one time and taken to UT Medical Center, police said. Initially, authorities said he had non-life-threatening injuries. But in the news conference late Monday, Knoxville Police Chief Eve Thomas said Wilson was in surgery and listed in serious condition.

"This wasn't a school shooting, this was an officer-involved shooting inside of a school, much different. At this point, the student hadn't done anything with the firearm until the officers engaged," TBI said. "It's important to make that distinction."

TBI said "there were no arrests I'm familiar with at this time," adding that "if anyone was detained, it's more than likely witness information."

Bob Thomas, Knox County Schools superintendent, said there will be counselors available in the school building tomorrow. He said while no classes will be held on Tuesday and Wednesday, a decision on the rest of the week's classes will come soon.

"We are all devastated by this tragedy," Thomas said during a news conference on Monday.

This is the fifth fatality surrounding the high school in the last few months and the community is "devastated," Corcoran Knoxville Fire Department Capt. D.J. Corcoran told CNN in an email.

Officials offer their condolences

Community officials weighed in on the tragedy on Monday, offering their condolences to Wilson and his family.

"Our hearts go out to the family of the deceased and to the officer and his family," Corcoran said. "Please pray for our community."

"He said that he'd rather that he be hurt than anybody else," she said.

Sen. Marsha Blackburn said she was "heartbroken to hear about the shooting."