Market Street in Watford was closed for more than two hours today, as firefighters extinguished a blaze in a flat above a sauna.
Witnesses reported seeing flames coming out of a window in the three-storey building just after 2pm.
Adam Smart, who works across the road in Pure DJ record shop, said he first saw smoke coming out of a window above Ace Health Club before an occupant in the building closed the window.
He said: "Five minutes later it just seemed to burst into flames again. The windows started smashing from the heat and the flames and three people ran out."
One man was treated for smoke inhalation at the scene. However, it is not believed anyone was seriously injured.
Firefighters appear to have extinguished the blaze on the first floor, but are still damping down the second floor.
The cause of the fire is not yet known.
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