Three fire engines were sent to the inferno, which started in a camper van before spreading to the Shell garage forecourt, at 9.30am this morning.
The fire is now under control, West Sussex Fire Rescue Service has said, adding that crews remained on the scene.
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A spokesman for Sussex Police said: ‘We have cordoned some of the area off and have evacuated nearby houses and businesses while we locate a gas leak.’
Residents are being asked to avoid the area.