Kingston Volunteer Fire Brigade Chief Fire Officer Tony Wilson said the cause was probably a spark from the Kingston Flyer.
The blaze started about 11.30am and took until 7pm to extinguish. Portable pumps had to be set up because the three appliances that attended could not access the area.
The area was partly Department of Conservation (Doc) land, and partly pastoral lease land. Doc also attended the blaze. The train underwent mitigation work yesterday to prevent more sparks escaping, and it could run as normal today, Mr Wilson said.