The school was placed on lockdown with entrance and exit roads blocked, Parsippany police said around 10:45 a.m.
Officers asked parents to avoid picking up their children but confirmed that all students were safe.
A 12 p.m. update from the department stated that the lockdown had been lifted and no weapon had been found.
“During the course of the investigation at PHHS by our School Resource Officers, it was determined that there was no weapon, specifically a gun, on school grounds or inside the school,” police said.
“It was determined that there was miscommunication amongst the students that led to the lockdown.”
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