Armed police stormed a high school in North Carolina after noises made by a malfunctioning heater were mistaken for an active shooter..

Pender County Sheriff’s Office told The Independent they had sent officers to investigate “reports of an active shooter” at Topsail High School in the town of Hampstead early on Friday morning.

A SWAT team searched the building and every school in the east of the county was placed on lockdown, but no gunman was found and no injuries were reported.

Authorities later confirmed the report was a false alarm.

“There’s no active shooter,” Tom Collins, the Pender County emergency management director, told local newspaper Star-News. “It’s a malfunctioning water heater.”

In a statement to news channel WECT, George Brown, chair of Pender County board of commissioners, said: “There is a piece of equipment at the school that has been malfunctioning in recent days that makes noise. It does sound like gunfire. This has been going on for several days."

He said police had been "taking this seriously and making sure".

The active shooter report came two days after 12 people were shot dead at a bar in California and nine months after 17 people were killed in Florida in one of the worst school massacres in US history.

Police were called to Topsail High School at 6.30am local time (11.30am GMT.)

Classes had not yet started but there are thought to have been some pupils in the school at the time.

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Local TV coverage showed police vehicles blocking the road leading to Topsail High School and a helicopter circling overhead. At least nine officers were also pictured on the school’s roof.

Buses carrying pupils to classes have been diverted to a safe area.