NEWTOWN, Conn. (CBSNewYork/AP) — Visitors were barred from Newtown High School in Newtown, Connecticut for the afternoon Tuesday, after school officials discovered a threat on social media.

Schools Superintendent Joseph Erardi sent an email to parents Tuesday notifying them of the lock-in at the high school.

READ MORE: Judge Lifts Temporary Pause On Vaccine Mandate For NYC Teachers And Other City Workers, Who Now Must Be Vaccinated By Monday

The lock-in allowed classes to continue on a normal schedule, but increases security and prevents visitors from entering the building.

The threat follows an evacuation last month at the temporary Sandy Hook Elementary School in Monroe following a threat received there. Building and grounds were checked following that threat, and no evidence of danger was found.

READ MORE: 'I Want A Proper Education': Some NYC Public School Students With Medical Exemptions From In-Person Instruction Feel They're Falling Behind

The original Sandy Hook Elementary School, since demolished, was the site of the December 2012 mass shooting that took the lives of 20 first-grade students and six educators.

Check Out These Other Stories From

[display-posts category=”news” wrapper=”ul” posts_per_page=”4″]

MORE NEWS: Mattress Giveaway In Queens Highlights Depth Of Need That Remains 3 Weeks After Ida

(TM and © Copyright 2014 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2014 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)