Freight companies are preparing for a huge spike in costs following Monday's quake.

Major South Island highways are either closed or badly damaged in many places, including State Highway 1 at Kaikoura, which would typically have 300 heavy trucks travel it every day.

The alternative route on the Lewis Pass between Christchurch and Picton will add 180km to the journey.

Road Transport Forum CEO Ken Shirley told Newstalk ZB's Mike Hosking Breakfast the changes to the freight routes have increased costs 18 per cent and will stretch an already overwhelmed industry.

Advertisement

"Road transport is a fiercely competitive industry... any increases [to the cost of freight] that are passed on will be fair and actual," he said.

"You can't expect a road transport operator to absorb the cost."

Shirley said it was expected 700 additional heavy trucks will be using the Lewis Pass every day and the resilience of the highway will be tested.