More than 20 schools are on lock-down as police hunt for an 'extremely dangerous' 18-year-old gunwoman.
The FBI and police officers are looking for 18-year-old Sol Pais who is believed to be armed.
Columbine High School - where two students murdered 13 people in 1999 - is one of the schools that has been shut in Colorado, USA.
Police tweeted: "The @FBIDenver & JCSO are asking for the public’s help regarding a potential credible threat. Last night Sol Pais traveled to Colorado and made threats.
"She is armed & considered to be extremely dangerous.
First picture of dad, 48, who died 'in play fight' outside nightclub
"She is a white female, 18 years old, approximately 5'5" in height, with brown hair.
"She was last seen wearing a black t-shirt, camouflage pants, and black boots. She was last seen in the foothills of Jefferson County.
"Please call the FBI tipline at (303) 630-6227 where your call will be answered immediately if you have seen this individual or have information on her whereabouts.
"Please do not approach her as she is considered armed and dangerous."
Elsie Frost murder secrets 'Beast of Wombwell' carried to his grave could be revealed
Jefferson County Sheriff's Office posted deputies at the locked-down schools with spokesman Mike Taplin confirming an FBI investigation was underway but declining to say more.
The manhunt come days after the twentieth anniversary of the massacre.
On April 20,1999, students Dylan Klebold, 17, and Eric Harris, 18, killed 12 students and one teacher in a mass shooting at Columbine.
The two shooters took their lives in the school's library.
