Staff were evacuated from a Barrow shipyard after a suspected hoax report of a bomb on a nuclear submarine.

BAE systems, which runs the Devonshire Dock complex that builds Britain’s nuclear submarines, confirmed that the site had been closed on Wednesday morning due to an “ongoing incident”. The defence firm later said nothing suspicious had been found in a sweep of the area.

A source told the Guardian that there had been an anonymous tip about a bomb on one of the Astute class vessels. Devonshire Dock is the oldest of the four docks that make up the Port of Barrow in Barrow-in-Furness, Cumbria.

A BAE Systems spokesman said on Wednesday morning: “We can confirm there is an ongoing incident at our Barrow site and we are liaising with Cumbria police, who are carrying out an investigation. As a precaution the Devonshire Dock complex has been closed. Staff, contractors and local residents are being kept informed.”

A police spokesman said they were assisting at the site. North West ambulance service said it was called to the scene at 9.18am. “We are currently on scene but there are no known casualties,” they said.

In a statement later Wednesday afternoon, BAE systems said: “Following an extensive sweep of the Devonshire Dock complex (DDC), including the four Astute class submarines in build, nothing suspicious was found. We expect to be able to close the incident shortly.

“Our first priority is always the safety of employees, the site and local residents, so in accordance with our emergency procedures, we made the decision to release personnel from the DDC earlier today. This was purely precautionary.”

The firm said it was satisfied there was no immediate safety risk and that employees due to come on site to start shifts after 4pm were being asked to report for work as normal.