Police were at Egg Harbor Township High School on Tuesday morning after the school received an unsubstantiated threat.
A shelter in place was activated "out of an abundance of caution," police said.
Parents received notification about the incident. A notice was also put out on the school's social media.
By 1 p.m., the threat was cleared, and classes resumed.
"While the threat has not been deemed credible at this time, we are taking all necessary precautions out of an abundance of caution to ensure the safety and well-being of our students, staff, and faculty," the school wrote on Instagram post about the shutdown.
The post explained that during a shelter-in-place all students and staff are to remain indoors, with all doors locked and windows secured. Outdoor activities and movement are restricted until further notice.
"Rest assured, our school security team, in collaboration with local law enforcement, is actively assessing the situation and taking appropriate steps to address any potential risks," the post continues. "While we understand that situations like these can be concerning, please be assured that the safety and security of our school community are our top priorities.
"We are closely monitoring the situation and will provide updates as necessary," the post reads.
Students in the comments seemed more concerned about getting to lunch than any safety issues.