Schools in Denver have closed after an 18-year-old "infatuated" with the Columbine massacre made threats and bought a shotgun and ammunition.

Police and FBI are hunting for Sol Pais after she flew into Colorado from Miami on Monday night.

She bought the weapons after arriving in the state and was last seen in the foothills west of Denver.

The teenager is considered armed and extremely dangerous and should not be approached, authorities said.

Saturday marks 20 years since two teenage gunmen murdered 12 classmates and a teacher then killed themselves at Columbine High School in a suburb of Denver.


At the time, it was America's deadliest school shooting.

Sol Pais is armed and dangerous. We are operating out of an abundance of caution. The threat is not isolated to one school or individual. Federal, state, and local law enforcement are working together to keep our community safe. Tip Line: 303-630-6227. Media Line: 303-630-6427. pic.twitter.com/KENVT1kEK3 — FBI Denver (@FBIDenver) April 17, 2019

All public schools in Denver were closed on Wednesday and afternoon activities and sports competitions were also cancelled.

Columbine High School itself and 21 nearby schools also put in place extra security on Tuesday, restricting entry and exit.

Dean Phillips, the agent in charge of the FBI in Denver, said the teenager was "extremely dangerous" but has not been charged with any crime.

He said Pais had made comments to others that made her a credible threat, but had not named a particular school.

"This has become a massive manhunt ... and every law enforcement agency is participating and helping in this effort," said Mr Phillips.

The FBI's Rocky Mountain Safe Streets Task Force described Pais as "infatuated with (the) Columbine school shooting".

Authorities tweeted pictures of her and said she was dressed in a black T-shirt, camouflage trousers and black boots.