A "modified" precautionary lockdown that prevented students and teachers from leaving the school buildings on Monday has been lifted, according to an updated alert on the district website.
All district schools were expected to be dismissed on time and all school activities were scheduled to resume, the alert said.
An alert issued on the district website earlier in the day said Hillsborough High School was under a modified lockdown. The original alert did not mention other schools in the district.
The original alert said there was no active threat and the lockdown was initiated as a "precautionary measure" as a result of a potential threat "by all appearances about a different town, but about which there is little further information," the alert said.
The alert said there was no "cause for concern."
The modified lockdown meant classes ran as usual within the building Monday, but students were not allowed to leave the building, the alert said.
An email to a Hillsborough district spokeswoman was not immediately returned.
Lt. Fran Mozgai, a spokesman for the Hillsborough Police Department, could only say the measure was precautionary and "due to an active investigation in another jurisdiction."
It was not immediately known if Hillsborough High's lockdown was related to what authorities said Monday afternoon was an "unfounded" threat of a gunman in Warren County, approximately 30 miles from Hillsborough.
The Hackettstown community was on lockdown as police and others searched for a gunman, who was believed to possibly be in the vicinity of Hackettstown High School. Students and workers at Centenary College, which is located in the town, received an automated alert saying police were looking for a white male in blue jeans and a black sweatshirt, with an assault rifle.
The college also said via its webpage that the situation began "when a man called the Warren County Communications Center about 9:45 a.m. and said he had an assault rifle in the woods beyond Hackettstown High School."
The Hackettstown high school was on lockdown, and nearby Washington Township (Morris County) schools implemented precautionary, security measures as well that were lifted by the end of the school day when the threat was determined to be unsubstantiated.