Passengers travelling to Greymouth on the Tranz Alpine train could have their travel plans disrupted this summer because the weather is too nice.
Already, one train has been held up because of the rail lines overheating, forcing the train to travel slowly, finally arriving at the Greymouth Railway Station at 3.15pm - two hours late.
On that occasion, heat sensors on the Midland Line showed temperatures on the rail lines reached 43degC.
Kiwi Rail says if the rail line temperature exceeds 40degC an inspection procedure is activated by the national train control centre before the passage of a train through the area. Track teams are also alerted and have to inspect the tracks before the train can continue its journey.
Kiwi Rail warns that over the coming summer months it is likely to impose speed restrictions on some sections of the line as a precautionary measure.