Students at a Midtown high school were barred from leaving their building Friday because of a disturbing mass-shooting threat — but police ultimately deemed the warning unfounded, according to the Department of Education.

Students at the High School for Environmental Studies in Hell’s Kitchen were AirDropped a message by someone threatening to go on a murderous rampage there, according to a self-described pupil who goes by Markk.s3 on Instagram.

“I’m going to shoot the school HSES at 11:30 a.m. [on] December 23 starting from the 6th floor down to floor 1,” read the threatening message.

“I will then take my own life in the middle of the gymnasium. For anyone seeing this, this is your last chance to run away.”

The high schoolers were placed on a so-called “hold” — which bars people from entering the school — around 10 a.m., according to the DOE and parents at the school.

The NYPD investigated and found the threat wasn’t credible and the measure was lifted at the school on West 56th Street near 10th Avenue, the DOE said.

A “hold” at a school is unlike a lockdown in that students were allowed to move around within the building once an “all clear” is given.

In March 2015, a 16-year-old boy was busted at the high school with a loaded gun. The .32-caliber revolver was tucked into his waistband, police said at the time.