The FBI and authorities in Colorado are looking for a woman "infatuated" with the 1999 Columbine High School massacre who they say poses a credible threat to the Denver-area community and schools — including Columbine.

All metro area school districts will be closed on Wednesday "due to ongoing safety concerns," Colorado's Department of Education said.

More than a dozen schools were placed on lockout in the Denver area on Tuesday at the department's recommendation after the woman traveled to Colorado earlier in the week. Lockout limits entry to and exit from the restricted schools, but leaves usual procedures otherwise in place.

The woman, identified as Sol Pais, 18, flew from the Miami area to Colorado, and investigators believe she bought a pump-action shotgun and ammunition after arriving, Dean Phillips, FBI special agent in charge of the Denver field office, said Tuesday night at a news conference.

Pais, a high school student in Miami Beach, then went to an area of the foothills where she was last seen, "and we have been trying to find her ever since," Phillips said.

"Because of her comments and her actions, because of her travel here to the state, because of her procurement of a weapon immediately upon arriving here, we considered her to be a credible threat — certainly to the community and potentially to schools," Phillips said.

"She has had an infatuation with Columbine and the perpetrators of Columbine," he said. "She has made comments to that effect, but she hasn't identified a specific threat to a specific school."

Phillips said that "her comments, her actions that we have heard about from others, tend to cause us great concern that she may pose a threat to a school — not necessarily Columbine."

He added, "Our priority in this situation is to try and find Ms. Pais."

The shootings at Columbine, in Littleton, which left 12 students and a teacher dead, occurred 20 years ago this week.

Pais, who is described as white and about 5-foot-5 with brown hair, was last seen wearing a black T-shirt, camouflage pants and black boots, said Mike Taplin, a Jefferson County sheriff's spokesman. He said that the sheriff's office was notified about the FBI investigation late Tuesday morning and that about 22 schools in Jefferson County, including Columbine, were placed on lockout shortly after noon.

Jefferson County school and sheriff's officials said that all students were safe and that most after-school activities were continuing as scheduled except at Columbine, where they were canceled.

No further details on the exception at Columbine were immediately available.

Jefferson County Sheriff Jeff Shrader said Tuesday night that "we take these threats seriously."

"It's certainly not the first threat that we’ve had that involves Columbine High School, or references it," Shrader said. "And in that regard, I know that this opens a wound, especially on an anniversary week, for those families who were most deeply impacted by this."