HAMPSTEAD, N.C. — Authorities in North Carolina said a reported active shooter at a high school was actually a malfunctioning water heater.

News reports quoted Pender County emergency management director Tom Collins as saying that noise from the water heater was taken for the sound of gunfire at Topsail High School in Hampstead on Friday morning.

The earlier report of shots fired provoked a massive response by law enforcement and caused the school district to reroute buses and put schools on lockdown.

Pender County Schools confirmed in a tweet that "noises heard coming from the top of the building" prompted the reports. It said law enforcement determined there was no shooter and no weapon. Topsail High, Middle and Elementary schools remained on lockdown, it said.

Capt. James Rowell of the Pender County Sheriff's Office was quoted as saying in local reports that deputies swept the school but found no evidence that any shots had been fired.

He said deputies did find an HVAC unit that was malfunctioning and making sounds similar to gunshots.

Reports of an active shooter came in around 6:30 a.m. According to Topsail High School's website, school begins at 8:30 a.m.

Topsail High School is located near the coast in Hampstead, about 20 miles north of Wilmington. It has around 1,300 students enrolled.

In May, an 18-year-old student was found in the school's parking lot with a large knife strapped to his leg and three other knives. A 16-year-old boy who authorities say armed himself with a semi-automatic rifle after hearing about that potential attack also was arrested.