No-one was injured in the incident, but around 60% of the building was damaged by fire, with the remainder affected by smoke. Crews used six jets, four hose reels and 30 sets of breathing apparatus to tackle the blaze.
The following day (Thursday) crews continued to damp down the ruins and go over the scene to eliminate any chance of re-ignition.
Fire and Rescue said an investigation into the cause of the fire was underway.
Welcome Break’s Rod McKie told BBC News: “We are extremely grateful to the firefighters who tackled the blaze and will assist with their investigations. The main amenities building in Fleet South will remain closed until further notice. Fleet North is fully open.”