The rail line is reopening to cope with an expected 'wall of wood'.

The mothballed Napier to Wairoa rail line is to come back to life late next year after a five-year hiatus.

KiwiRail and Napier Port announced a commercial agreement on Thursday that would see the port company run a dedicated log service from Wairoa to the port from late next year.

The agreement depends on the port company approving KiwiRail's updated forecast cost for restoring the line to service.

The line has been mothballed since 2012, when wash-outs on the Wairoa-Gisborne section led KiwiRail to stop all rail services north of Napier.

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Port chief executive Garth Cowie said the East Coast region was expecting a major increase in log exports from late next year, with significant volumes forecast to come through both Eastland Port in Gisborne and Napier Port.

"The increasing long-term log volumes from Wairoa will stretch the capacity and infrastructure of both road and rail in the whole East Coast region," he said.

"It's vital that we have the capability within the wider region to transport these in a reliable, efficient and environmentally friendly manner, and the reopening of the rail link will enhance transport options for our log exporters."

The Wairoa log service will initially run over the weekend, with two services each Saturday and Sunday.

KiwiRail chief executive Peter Reidy said: "We had always signalled that the line could reopen in the future, as long as there was sufficient freight volume available to support rail operations and the necessary investment in infrastructure was made".

The port is owned by Hawke's Bay Regional Council. Interim chief executive Liz Lambert was delighted.

"The community regularly gave us feedback supporting this line being reinstated. It makes perfect sense to see this arrangement sit commercially between Napier Port and KiwiRail."