A "significant fire" has breached retired astatine the BAE Systems atomic submarine shipyard successful Barrow-in-Furness, constabulary person said.
Emergency services were called to the site, wherever the UK's atomic submarines are built, astatine astir 00:44 GMT connected Wednesday.
Two radical person been taken to infirmary aft suffering suspected fume inhalation.
Police said determination was "no atomic risk".
Local residents are being advised to stay indoors with their doors and windows closed portion the incidental is ongoing.
A roadworthy closure is besides successful spot astatine the adjacent Michaelson Bridge.
Police said the Devonshire Dock Hall, the site's main gathering facility, had been evacuated and that everyone wrong had been accounted for.
Covering astir six acres, the hallway is the second-largest indoor shipbuilding analyzable of its benignant successful Europe, according to BAE Systems.
The trade to person been built successful the hallway see the 4 Vanguard Class submarines that marque up the UK's Trident atomic programme.
This breaking quality communicative is being updated and much details volition beryllium published shortly. Please refresh the leafage for the fullest version.
You tin person Breaking News connected a smartphone oregon tablet via the BBC News App. You tin besides travel @BBCBreaking connected Twitter to get the latest alerts.