Six fire engines and 35 firefighters tackled a fire in the Vision Express shop in Ruislip High Street on Monday (February 22) evening.
According to London Fire Brigade, the alarm was raised by people in a neighbouring shop who noticed smoke pouring into the front of their own property.
The damage to the shop means it will be closed for repairs, with a temporary alternative shop open in Ruislip in the meantime. It is located in a former Gregs bakery store just three doors away at 106 in High Street.
When the first fire crew arrived, they discovered the fire at the back of the shop with the blaze spreading to a flat above.
The shop and flat were both reportedly left severely damaged by the fire, but LFB confirmed that there were no injuries and nobody was inside at the time.
Daniel Hardman witnessed the fire and told getwestlondon : "I was walking up towards the train station and there were fire engines in the road and smoke coming up above Vision Express.
"Caffe Nero had smoke inside and a hose was going through Baskin-Robbins next door.
"All the flats above had smoke in them too and there were loads of fire engines around, I couldn't make out where the fire was coming from.
"Firefighters had to break through the door at Vision Express to get in."
London Fire Brigade was called at 7.20pm, with the fire being brought under control by 10.56pm.
A smoke alarm was said to have been fitted, but it is not known if it operated.
A London Fire Brigade spokesperson said: “It is important to make sure your smoke alarm is always working properly, and that the batteries have not been removed.
"Everyone should have at least one smoke alarm on every level of their home and the safest option is have those linked together. This will give the earliest warning if there is a fire."
A Vision Express spokesperson said: “The Ruislip store will remain closed while the cause is determined and the store is refurbished."