Fire crews were called to the Booths in Chorley yesterday evening (Tuesday, 29 November) after it suffered its second fire related incident in a week.
The incident was first reported by passersby at around midnight last night after they spotted smoke rising from the three-storey building in New Market Street.
It is thought that another gas heater caught fire on the roof of the shop.
Night workers were evacuated from the store and nobody was injured during the incident.
Crew Manager Ian Turnbull said: "If we hadn't attended as early as we did there was a real danger that the fire could have spread to the shop."
There was no damage to the store which was open as usual this morning.
A spokesperson for Booths said: "A second small fire on the roof in the second heating plant at Booths in Chorley last night.
"The incident happened overnight while the store was closed and was under control swiftly thanks to staff and the fire brigade.
"The safety of our staff and customers is paramount and again all safety procedures were followed and the incident was under control quickly. There is no damage to the shop floor and the fire only affected a small element of the roof.
"Gas and power supplies to the roof have been isolated as an additional precaution, which will result in the store being colder than usual."