BAE Systems, which is also the UK's biggest engineering company, said the blast happened at its site in Glascoed, Monmouthshire, South Wales, on Wednesday morning.

A spokeswoman from the arms manufacturer said no one had been injured and everyone had been accounted for.

"We can confirm that there was an incident at our Glascoed facility in Wales this morning," she said.

"Tried and tested safety protocols were immediately enacted and emergency services attended the site.

"All personnel are accounted for and there were no injuries.

"Our emergency response team continue to monitor the facility and a full investigation has been launched."

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About 550 people work at the Monmouthshire site which was established to help the Royal Navy prepare before the Second World War.

BAE Systems, one of the world's biggest defence contractors, produces a huge array of military hardware and technology - including nuclear submarines, fighter jets, tanks and ships, as well as guns and ammunition.

It also builds type 26 frigates for the Royal Navy and makes electronic warfare systems for F-35 fighter jets.

In 2023 the company enjoyed a record year for new orders as Western governments stepped up defence spending in response to Russia's attack on Ukraine.