Heavy truck traffic is expected to increase through the West Coast after the 7.5 magnitude earthquake.

Lines of large trucks and trailers started arriving in Greymouth yesterday, and traffic was building through Springs Junction this morning as the ferry sailings resumed.

The New Zealand Transport Agency said State Highway 7 between Springs Junction and Waipara was open, although down to one lane in places. With heavy rain, strong winds and aftershocks, the risk of further slips and rockfalls in the area was high.

The Arthur's Pass route has some cracking and temporary speed limits in places.

Springs Junction service station GAS Lewis Pass proprietor Steve Templeton said he was expecting business to boom now the Lewis was open again.

It was obvious heavy freight trucks would be diverted through as a result of the main South Island freight routes from the Cook Straight ferries to Christchurch being blocked.

"It's starting this morning to get busier and busier," Templeton said. "It's the trucks coming through ... this road is going to be busier."

He had ordered in extra fuel and supplies, particularly diesel, and expected he would need to find extra staff given that State Highway 1 between Picton and Kaikoura was "a mess" and could be closed for months.

The Lewis Pass had a few slips but no major damage, however, "I don't know how well it's going to stand up to all the trucks"

Templeton said it would be amazing to see more trucks through, although the route ordinarily saw oversized freight carriers due to the tunnel restrictions on State Highway 1.

Other motorists on the road would need to "take it easy" given instability in some places, he said.

Meanwhile, Greymouth New World owner-operator Victoria Boyes today reassured there was no need to panic buy, despite some small delays in deliveries yesterday.

Foodstuffs South Island supply chain general manager John Mullins said everything was "as normal as they can be" in terms of supplying the West Coast New World and Four Square supermarkets from Christchurch.

"If anything there is a bit of a run on water, which is typical of these events," Mr Mullins said.

With the ferries now running this morning transport of stock into the South Island for distribution was returning to normal. Foodstuffs also relied on coastal shipping into Christchurch and Dunedin for a good part of their supply.

Mullins said they were sending their supply trucks for Nelson and Marlborough via Greymouth.

They also expected to send some supplies into Kaikoura today by helicopter. The HMNZ Canterbury would also take some supplies and the Inland Kaikoura route was expected to reopen within five days, he said.

All trains running on the West Coast rail network were given the green light by yesterday afternoon, with a delayed freight train for Hokitika passing through Greymouth early afternoon.

Kiwi Rail West Coast network manager Chris Stoop said all lines had been given the all-clear and the Tranz Alpine was running as normal today.

Kiwi Rail said the Kaiarahi and Kaitaki ferries were scheduled to sail between Wellington and Picton today carrying freight and vehicle passengers only; foot traffic has been suspended due to terminal damage.

Today the country's freight companies were making contingency plans for the South Island.

Mainfreight chief executive Don Brain told NZME they were turning to coastal shipping to continue their South Island operation.

- Greymouth Star