A blaze which took hold of a bungalow and caravan in Leverstock Green has now been put out after what was thought to be a chip pan fire.
A crew from the town’s fire station battled the flames at September Cottage off Leverstock Green Road, Hemel Hempstead, for more than an hour.
Police closed the road to traffic, causing tailbacks towards the M1, and traffic control measures are still in place allowing vehicles through one lane at a time.
Emergency services were alerted to the scene at around 3.15pm and the flames had been quelled by 4.30pm.
Eyewitness Irene Benedickter said she was unable to access her own home, near the scene, for half an hour before finally being allowed to mount the grass verge to pass.
She said: “There is a thick smell of smoke, we could smell it in the car.
“Somebody said it was a caravan but you can’t see the damage.”
Firefighters are due to re-inspect the scene this evening at 7pm to confirm the cause of the fire.