Crews rushed to the Cartridge World shop in George Place, Bathgate, following a call received shortly after 9am this morning.
The blaze was tackled by dozens of fighters using hose and breathing apparatus.
Road closures were put in place, at Glasgow Road and the junction of Whitburn Road and the Fairway hotel.
Firefighters - who were joined at the scene by senior officers - described the building was “well alight”. At around 10.50am, crews managed to gain access to the store’s roof space, which was checked for fire spread.
Staff in a neighbouring property were also evacuated, but it is understood they have been allowed to re-enter.
There were no reports of casualties.