Emergency services have been scrambled to the blaze at Sir Robert Peel Hospital in Tamworth, Staffordshire.
The fire is tearing through the George Bryan Centre at the hospital – a facility that treats people mental health issues.
Dramatic pictures show large flames engulfing the building with thick black smoke billowing into the air.
Staffordshire Fire & Rescue Service have confirmed 10 fire engines are at the scene.
Locals are taking to Twitter to voice their shock at the blaze.
One wrote: "Thoughts with all concerned. Hope no one hurt.
"Looks massive the fire. I did so much work to keep this service open with the trust. Very concerning and yet another fire in Tamworth."
Another said: "Oh my God, hopefully everyone got out safe and no one is harmed."
And a third wrote: "Just heard about the fire at Tamworth hospital, please if anyone can, go down and comfort those people outside, they’ll be a lot of sick patients there who will need some security!"
A fourth posted: "Shocking scenes. Tamworth’s only mental health provider @NHSEngland, on fire. Hope everything’s okay."
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