Firefighters are battling 19 separate fires around a 12-kilometre stretch of railway track south of Oamaru tonight.
The fires, which were first reported at about 2.30pm today are believed to have been sparked by a 69-year old steam engine taking 400 passengers on a return trip from Dunedin to Oamaru.
Principal officer of the Otago Rural Fire Authority, Stephanie Rotarangi, said five crews and three helicopters are on site.
She said although the fires are still burning, and crews will have to remain there overnight, the spread has been contained.
Dunedin Railways says it will investigate whether the steam train started the fires which temporarily closed parts of State Highway 1 and threatening crop fields.
Chief executive of Dunedin Railways, Murray Bond, said the company had planned carefully before taking the steam locomotive on a trip.
"We had understood that rural fire was pleased with the planning work we'd done, as we have to do for all such trips.
"And that's what we need to investigate, because something may have gone wrong with the locomotive just south of Oamaru and we don't know that, so we need to investigate the causes. "
Mr Bond said he believed the company had not taken a steam engine on that particular journey for about 20 years.