LITTLETON, COLORADO – Multiple law enforcement and fire agencies are at Columbine High School after a caller with a male voice phoned in a threat about multiple explosives inside the campus and a man outside with a gun.

As a precaution, Jefferson County Public Schools increased security at 24 campuses, with Columbine HS on a lockout.

A complete search of the high school has found no evidence of any credible threat to the campus. All students and staff are safe, according to the Jefferson County Sheriff’s Office.

There is a high likelihood this is all tied to reported nationwide threats across the country towards schools and businesses as part of a nefarious phishing scam. NBC News in reporting the emails or messages receive threaten violent action unless the victim transfers Bitcoin to a specified account.

At Columbine HS, all students will remain inside as entry and exit are restricted until the campus is cleared. Parents can expect to be reunited with their children at 2:45 p.m., the normal end of the school day.

In the meantime, people are still advised to avoid the area.

UPDATE: ALL CLEAR at Columbine High School. Investigation remains ongoing. We’re still trying to determine the location of the caller. However there is NO direct threat to Columbine HS pic.twitter.com/3byOUdTz0x — Jeffco Sheriff (@jeffcosheriffco) December 13, 2018

A spokesperson for the school system says they get several threats a year at the campus. Specifics on why this incident was handled with a significant response from law enforcement was not revealed.

The location is the same site where 13 people were killed by two student gunman who took their own lives rather than be arrested by police in 1999.

There was a similar incident in Summit County where the sheriff’s office says several 911 calls and Safe2Tell tips starting coming in late Wednesday afternoon out of concern for Summit High School.

No danger was found at the campus while additional law enforcement personnel were on scene. So far, the sheriff’s office has not detailed where the original comments about a potential threat originated.