Two people have been taken to hospital after a “significant” fire broke out at BAE Systems’ nuclear submarine shipyard in Cumbria.

Residents said they saw huge flames and smoke billowing from the complex in Barrow-in-Furness, where the UK’s new multi-billion-pound Dreadnought submarines are being built.

Cumbria police said there was no nuclear risk but two people were taken to hospital for suspected smoke inhalation. Police said: “At this time there are no other casualties and everyone else has been evacuated from the Devonshire Dock Hall and are accounted for.”

BAE said the two people taken to hospital were workers at the site and they have since been discharged. About 200 people were working on a night shift at the time the fire broke out.

Naval sources and investigators played down the possibility the fire was suspicious and related to Russia, though inquiries were acknowledged to be at an early stage.

A Ministry of Defence (MoD) spokesperson said it was working closely with emergency services and BAE Systems and added: “We would like to thank the emergency services for their swift response and wish those who have required hospital treatment a quick recovery.”

Images posted on social media overnight showed flames shooting out from the Devonshire Dock Hall building, with alarms blaring in the background.

The six-acre site, which has towered over the Cumbrian skyline for nearly 40 years, is one of the biggest and most advanced shipbuilding sites in the world. First opened in 1986, Devonshire Dock Hall is the primary construction site for the UK’s trident nuclear programme and is almost large enough to house the Titanic.

Four nuclear submarines from the Dreadnought class are being built there as part of a £31bn programme, which is due to replace the Vanguard submarines in the early 2030s. The last of the Royal Navy’s seven new nuclear-powered submarines, part of the Astute class, is also being built at the site.

It is understood that the boat in the hall is HMS Agincourt, whose completion had already been delayed to 2026. The previous Astute class, HMS Agamemnon, was launched last month. It remains unclear whether any submarines were damaged by the fire.

The MoD has been contacted for comment. Cumbria fire and rescue service said an investigation into the cause of the fire was under way.

Police on Wednesday advised residents to keep doors and windows closed, having earlier instructed people to stay indoors. Motorists in the area have also been told to close their windows, air vents and sunroofs and turn off fans and air-conditioning units.

It is understood that the warning was because of the risk of particles, such as those from metals, being released in the air from the heavy industry site, where sophisticated extraction techniques are normally in place.

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A woman who lives beside the shipyard said she saw thick black smoke billowing from the building. Donna Butler, 36, said: “My son came and got me and said that the BAE alarms were going off, so we went. When I opened the front door, we just saw a lot of black smoke. It was a lot of black smoke, like really thick black smoke, and it was very loud.”

BAE Systems reportedly told non-essential staff working at Devonshire Dock Hall to work from home on Wednesday, while the BBC reported that staff turning up for their shifts were confused as to which parts of the 25,000 sq metre site was accessible.

Shares in BAE Systems fell as much as 2% in morning trading after news of the fire, making it one of the biggest fallers on the FTSE 100 index of blue-chip companies.

A BAE Systems spokesperson said: “The area around the Devonshire Dock Hall has been evacuated and everyone has been accounted for. Two colleagues were taken to hospital having suffered suspected smoke inhalation and have both since been released.”

It is understood that the company will launch an investigation into the cause of the fire. The rest of the site remains open and operating normally.

Additional reporting by Dan Sabbagh