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An 18-year-old woman suspected of making threats to Denver-area schools has been found dead, the FBI says.

Sol Pais was reportedly obsessed with the 1999 Columbine high school massacre, in which two teenagers murdered 12 students and a teacher.

The alleged threat led to school closures for half a million students and a manhunt for the Florida woman.

She allegedly travelled to the state and bought a shotgun ahead of the 20th anniversary of the Columbine shooting.

Jefferson County Sheriff Jeff Shrader said on Wednesday that she died from an apparent self-inflicted gunshot wound, the Associated Press reported.

The FBI earlier tweeted there was no longer a threat to the community and the suspect is deceased.

Officials said at a news conference that local schools would reopen on Thursday and events marking the anniversary of the 1999 shooting would continue on Saturday.

Nearly 30 armed officers swarm the woods near the Echo Park Campground in the Arapaho National Forest, CBS News reports.

The Echo Lake Lodge, nearby to where she was reportedly found, does not open until late May due to weather.

She travelled to Denver from Miami on Monday night and purchased a pump-action shotgun and ammunition, the Jefferson County Sheriff's Office said.

Police had considered her armed and extremely dangerous.

Witnesses told local media that she was seen running naked and armed with a gun in the area earlier on Wednesday.

The suspect's family had urged her to turn herself in as authorities launched a manhunt.

"It's like a bad dream. We don't know. We don't have any ideas," her father told CBS News in Miami.

Police say Pais made statements to friends and family and had posted online about her fascination with the Columbine shooting.

According to the news outlet, more than 130 schools in and around Denver had closed as officials searched for her.