KiwiRail anticipates the rail link between Canterbury and the West Coast could be out for at least six weeks following fire damage at the weekend.
The fire has damaged bridges, track and signal systems and affected services, including the TranzAlpine journey, plus coal and dairy freight services.
The large blaze broke out on conservation land between Cass and Springfield early on Saturday near the rail bridge over Broken River.
About 300ha of scrub was destroyed and the cause of the fire is still unknown.
KiwiRail network services group general manager Todd Moyle said crews from around the country would be brought in to tackle the line reinstatement as soon as possible.
"Hot and windy conditions at the weekend meant several of our bridges along the route were damaged, including one bridge where 12 wooden piles will need to be replaced.
"We are still working through the quickest course of action to reinstate the line.
"We are very disappointed for the many international tourists who ... will now miss out on the ... TranzAlpine service.''
Grey district Mayor Tony Kokshoorn said if the line continued to stay closed, tourism in Greymouth and the wider West Coast would be significantly affected.
There are three main users of the Christchurch-Greymouth line. The TranzAlpine train makes the daily return trip.
Westland Milk Products transports milk to and from its factory in Hokitika, and Solid Energy rails Stockton coal to Lyttelton for export.
