LOS ANGELES — Schools in the US city of Denver closed on Wednesday amid fears that an armed woman obsessed with the Columbine High School massacre 20 years ago poses a “credible threat.”

US authorities have mounted a massive search for Sol Pais, 18, who traveled from Florida to Colorado where she reportedly purchased a pump-action shotgun and ammunition.

“She is armed and considered to be extremely dangerous,” the Jefferson County sheriff’s office said.

Security fears have soared because Saturday is the 20th anniversary of the massacre, at the time the deadliest school shooting in US history, which unfolded in the Denver suburb of Columbine.

Two heavily armed gunmen killed 12 fellow students and a teacher before taking their own lives on April 20, 1999, setting off an era of mass shootings in US schools and other public venues.

“Metro area school districts will be closed on Wednesday, April 17 due to ongoing safety concerns,” the Colorado Department of Education announced on its Twitter account.

That was a step up from Tuesday when it put Denver area schools on lockdown following an alert from the FBI and stepped up security.

Authorities have posted pictures of Pais, her unsmiling visage framed by shoulder-length brown hair.

She was last seen in Colorado on Monday night, the sheriff’s office said.

“We are operating out of an abundance of caution. The threat is not isolated to one school or individual,” Colorado’s public safety department said on Twitter.

“Federal, state, and local law enforcement are working together to keep our community safe.” — AFP