Two fire crews rushed to reports of a fire at Asda in Hillfield Road, Hemel Hempstead.
Emergency services were called just after 9.30am this morning (Wednesday) and the supermarket was evacuated – but customers were allowed back in within 20 minutes.
Asda grocery worker Chris Ward, who helped evacuate customers, said: “Something in our deli oven caught fire, which made a lot of smoke, setting off the automatic fire alarm to the fire station.”
He said the smoke was contained and did not spread to the public area of the store. Firefighters are now investigating the cause of the blaze.