A cigarette butt may have started the small grass fire next to the Lowburn Bridge on State Highway 6 near Cromwell yesterday afternoon.
The fire, which covered 20m by 10m, was quickly brought under control by the Cromwell Fire Brigade.
Senior Station Officer John Searle said the cause was unknown but he suspected it could have been a cigarette butt thrown from a vehicle, as the fire started next to the road.
''Things are getting pretty dry out there, so people need to be careful,'' he said.
