A huge blaze broke out in the early hours at BAE Systems' shipyard that builds Britain's nuclear submarines but there is no major risk from the incident, police said on Wednesday.
Pictures online showed what looked like flames and black smoke emerging from the top of the vast Devonshire Dock Hall building.
Cumbria police in northwest England said two people had been taken to a hospital after suffering from suspected smoke inhalation and there were no other casualties.
"There is no nuclear risk," police said. "However, people living nearby are advised to remain indoors whilst emergency services respond to the incident and keep doors and windows closed."
Shares in BAE Systems were trading down 1.7 per cent in early deals.
Police said the emergency services were called to the site at 0044 GMT.
BAE Systems, Britain's biggest defence company, said it was working with emergency services to deal with the fire. It said one of the two people had since been released from hospital.
"The area around the Devonshire Dock Hall has been evacuated and everyone has been accounted for," a spokesperson said.
The site has built some of Britain's most significant marine vessels and it employs around 10,000 people to work on the Astute and Dreadnought classes of nuclear powered submarines.
Covering around 6 acres, it is the second biggest shipbuilding complex of its kind in Europe, according to the company.
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