North Brunswick Township High School was locked down for several hours Wednesday morning after receiving a threatening message.

School officials say the principal received a message on the school?s answering machine that contained the words ?shoot up the place.? The school was locked down after 7:30 a.m. and police from surrounding towns were contacted.

Students were instructed to leave their backpacks outside classrooms to be inspected by police and K-9 units. Parents were allowed to pick up their students, but were only allowed in five at a time and had to show identification before taking their child home.

Classes resumed after the lockdown was lifted just before noon. The school held an informal meeting Wednesday night for parents. At the meeting, parents expressed frustration about the school's communication with them.

Click here to watch more on parents' reaction to the incident