WTVD reports the call came in at about 6:30 a.m. Friday morning.
"There's no active shooter", Collins said.
James Rowell with the Pender County Sheriff's Office confirmed there were no reports of injuries Friday.
The situation was unfolding at Topsail High School in the unincorporated town of Hampstead, North Carolina, reported WECT, a television station in Wilmington.
Police said there are now no reports of injuries.
News reports quote 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 on Friday morning.
Commissioner George Brown told WECT that there is a piece of equipment at the school that has been malfunctioning recently and sounds like gunfire when it makes noise.
Norwegian frigate could sink after being rammed in harbor
Eirik Walle, of Norway's rescue centre, told Norwegian news agency NTB the collision smashed a hole in the side of the warship. The frigate is part of a Nato fleet in the Atlantic and the alliance has been informed of the accident, he told reporters.
A Pender County dispatcher told Reuters that deputies were responding to a situation at a local high school, but could not elaborate.
School buses have been corralled at the Lowes Foods parking lot across from the school campus.
Reports of an active shooter at Topsail High School are said to be due to faulty mechanical equipment.
All of the schools in the district have been placed in lock down.
It shares a campus with a middle school and an elementary school.
The school district said that parents who planned to drive their children to school should not do so. It has around 1,300 students enrolled.