A lockdown and an unspecified threat thwarted plans for students at two South Jersey high schools to take part in the National Student Walkout to protest gun violence in the wake of the Parkland, Fla., mass killing a month ago.

The lockdown occurred at the Atlantic City High School after a student notified a staff member that weapons may have been hidden on the school's campus, Atlantic City police said.

Police officers and state troopers, who were already at the school as an added layer of security for the anticipated student protest, put the school in lockdown. With K-9 units, they searched inside and outside the school, police said.

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No weapons were found and several students were interviewed by detectives as "potential witnesses," police said in a statement.

Students were sent home on buses and after-school activities were canceled.

Earlier, the Clearview Regional School District in Gloucester County canceled classes for the day after Harrison Township police reported a threat against the district's high school.

The district, which has about 2,500 students in grades 7-12 from rural Harrison and Mantua Townships, said in a statement that county Sheriff's Department officers and state police canine units conducted a sweep of the school building overnight but found no weapons.

Still, the district said, it decided to close for the day "due to the lack of specificity to the threat."

Thousands of students throughout the Philadelphia region took part in walkouts to protest gun violence and mark the deaths of 17 people in the shooting Feb. 14 at the Marjory Stoneman Douglas High School in Parkland.