Stone Bridge High School in Ashburn VA evacuated

Police have given the all-clear for several northern New Jersey school districts that received bombs threats Friday morning.

The threats came by robocall between 11:22 and 11:50 a.m., WUSA9 journalist Surae Chinn reported.

According to officials,"robo-call" bomb threats have become an issue nationwide.

The majority of the threats were in Bergen County.

Students at Stone Bridge were back in school by 1:40 p.m. after the Loudoun County Sheriff's Office completed a sweep of the building and declared it safe, according to the Loudoun Times-Mirror. A spokeswoman said the media is not allowed to attend.

Dwight Morrow in Englewood, Teaneck, Paramus Catholic, Oradell, Mahwah, Waldwick, and Hackensack, said sheriff's spokesman Anthony Cureton. Students in some schools were evacuated, while other schools chose to lock down.

"Police are still clearing the school ... but nothing suspicious has been found so far", Troxell said.

In Fairfax County Public Schools, Westfield High School, McLean High School and Herndon High School received threats around the same time. All of the calls were deemed to be hoaxes, and the FBI is assisting local authorities in the investigation.