A fire at the Queen Elizabeth University Hospital (QEUH) in Glasgow was likely caused by a discarded cigarette, according to the health board.
The Scottish Fire and Rescue Service were first called to the scene at 9.22am on Wednesday, with four appliances were in attendance.
But security crews had already extinguished the flames outside the building.
NHS Greater Glasgow and Clyde said it had likely been caused by a discarded cigarette.
A spokesman said: “This morning at around 9.20am, our security teams provided an immediate response to a fire alarm at the QEUH and extinguished a small fire outside of the main building.
“The fire was accidental and likely caused by an inappropriately discarded cigarette.
“Thanks to our established fire safety protocols and the quick response of our team, there were no injuries and the fire was quickly extinguished.
“While the fire service completes necessary follow-up assessments and safety checks, a number patients and staff have been temporarily evacuated from the building.”