Schools in and around Denver, Colorado, will be closed on Wednesday as the authorities continue a massive hunt for an 18-year-old woman suspected of making threats against Columbine high school, just days before the 20th anniversary of the mass shooting.

Police in southern Florida, where she lives, were searching her home on Wednesday morning.

Officers were seen removing large stacks of papers from the single-family home of the young woman, Sol Pais, in Surfside, a city just north of Miami Beach.

School officials say Pais is a student at Miami Beach high school.

The threats prompted a lockdown at the high school for around three hours on Tuesday afternoon, as well as at more than 20 other schools in the Denver area.

The @FBIDenver & JCSO are asking for the public’s help regarding a potential credible threat. Last night Sol Pais traveled to Colorado & made threats. She is armed & considered to be extremely dangerous 1/3 pic.twitter.com/2x5iwddsMp — Jeffco Sheriff (@jeffcosheriffco) April 16, 2019

According to Jefferson county sheriff’s office and the FBI, Pais, traveled to Colorado from Florida on Monday. She made threats of an undisclosed nature, as well as purchasing a pump-action shotgun and ammunition.

Officials have said Pais was “infatuated with [the] Columbine school shooting” and should be considered “armed and extremely dangerous”.

The authorities say her fascination with the Columbine shooting and the two perpetrators, and recent actions, raised suspicions.

They said she should not be approached, and is considered extremely dangerous, but did not provide further details about the nature of the threat. She was believed to be in the Denver-Littleton area and “attempting to buy firearms”.

In 1999, two students at the school in Littleton, near Denver, came on to the premises heavily armed and shot students and teachers, killing 13. The perpetrators also died in the attack. The massacre ushered in the modern era of frequent mass shootings at schools in America.

All schools in the Denver area were urged on Tuesday to tighten security because the threat was deemed “credible and general”, said Patricia Billinger, a spokeswoman for the Colorado department of public safety.

“We always have heightened awareness close to high-profile anniversaries like this,” Billinger said.

Pais was last seen in the foothills of the Rocky Mountains, west of Denver, was considered armed and extremely dangerous and should not be approached, authorities said.

“This has become a massive manhunt … and every law enforcement agency is participating and helping in this effort,” Dean Phillips, special agent in charge of the FBI in Denver, said late on Tuesday night.

The FBI’s Rocky Mountain Safe Streets Task Force issued a notice on Tuesday describing Pais as “infatuated with [the] Columbine school shooting.” The alert also said police who come into contact with her should detain her and evaluate her mental health.

Sheriff’s spokesman Mike Taplin said the threats she made were general and not specific to any school.

The Denver Post reported that a call to a phone number listed for Pais’s parents in Surfside, Florida, was interrupted by a man who identified himself as an FBI agent and said he was interviewing them.

Sgt Marian Cruz of Surfside police confirmed that the 18-year-old’s parents last saw her on Sunday and reported her missing on Monday. The Miami Herald and WTVJ are reporting that neighbors say the teen is a senior at Miami Beach high school.

The current threat comes just days before the 20th anniversary of the Columbine school shooting, during which two students shot and killed 12 of their classmates and a teacher.

In December, an anonymous caller claimed bombs had been planted inside Columbine high school. The threat, which was found to be a hoax, triggered an aggressive police response.