Northland's only surviving railway line will be mothballed north of Kauri because KiwiRail says it is no longer viable.

Currently the North Auckland rail line starts in Auckland and passes Helensville, Whangarei and the dairy plant at Kauri, ending at a log loading yard at Otiria, near Moerewa.

However, leaked documents show KiwiRail plans to mothball the northernmost section of the line in September.

The only customer north of Kauri, the woodchip company Marusumi, was informed its contract would not be renewed after August because of poor commercial returns and "life-expired wagons".


Currently two trains use the northern part of the line each day. From September Marusumi's logs will be hauled to its Portland mill by road.

KiwiRail insists the line will not be closed but once it is no longer used or maintained it is likely to deteriorate further.

The news caught Transport Minister Simon Bridges by surprise. He insisted the Government had no intention of shutting any lines but said there was little or no demand for the line at present.

"In that sense, we can see KiwiRail's perspective where they are seeking to run a commercial business," he said.

Northland MP and NZ First leader Winston Peters was sceptical about assurances the line would remain open even though it would not be used after September 1.

"In Parliament the PM claimed that the main customer was not renewing the contract, but the line was open for use by any other business ... The fact is the Government is running down the line north from Whangarei - trains are being stopped, the weeds will grow, the track will deteriorate and it will never be cost effective to use it again, but it will still be open according to the PM."

"If that is the case then the Dargaville to Whangarei line is still open, though a quick look at its condition would suggest otherwise," Mr Peters said.

When the Government launched its 58-point action plan for boosting Northland's economy last month, Northland-based Green MP David Clendon noted it made no mention of rail and questioned whether that meant National saw no future in trains.

Economic Development Minister Steven Joyce said the plan focused on initiatives that could be taken in the short to medium term. Rail was considered a longer term option but its viability depended on greatly increased freight demands and the effect of a new container terminal at Northport.

Mothballing of the northern section of the line, with access to large areas of pine forest, is another blow to plans to build a rail link between the Northland line and Northport.

The mothballing follows the closure of the Dargaville branch line in October last year. The Opua branch was last used for freight in 1985 and is now being restored for use by the Bay of Islands Vintage Railway. The Okaihau branch was last used in 1983 and pulled up in 1987. The corridor is now used for a cycle trail.