Motorists are being warned of big traffic delays on upper South Island roads this summer after landslips cut off the main highway.

The New Zealand Transport Agency (NZTA) said today that the closure of State Highway One near Kaikoura has created new traffic and safety concerns on the alternative route, via the Lewis Pass and Murchison.

Speaking at a press conference at Parliament, NZTA regional performance manager Mark Owens said the Lewis Pass route would have to be upgraded to cope with the rise in traffic.

"The reality is, this will be the main highway connection for this part of the country for some time."

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Owens warned motorists it was a longer, more challenging road, which was "windy in places", and included several one-lane bridges. Drivers were urged to plan ahead and leave plenty of time for their journeys.

Motorists driving between Picton and Christchurch should now expect the journey to take at least 7.5 hours - around two hours longer than the coastal route.

Owens said the sudden upsurge in traffic on the route, especially trucks, has upset residents and created new safety concerns.

As a result, new speed restrictions have been introduced and the police presence has increased on the alternative route.

Speaking about SH1, Owens said clearing the main route was a "huge job" and would take "at least several months".

Some of the smaller slips on the highway were already being cleared. But ongoing aftershocks meant it was still too dangerous to assess the larger slips, the scale and complexity of which were "unprecedented" in New Zealand.

Each of the seven landslips on SH1 were as large as one in Manawatu Gorge in 2010, which cost $35 million to clear up.

The inland route to Kaikoura was expected to be reopened in the next few days.

Its closure has angered some local farmers, who believe it is safe and they are being blocked from using it unfairly.

Owens said the road was still "a high risk worksite", and allowing public access would delay its reopening.

Paua, crayfish ban

Catching paua and lobster near Kaikoura has been banned because of the damage to the species' habitat caused by last week's earthquake.

Primary Industries Minister Nathan Guy announced closures to the shellfish, crayfish and seaweed fisheries this afternoon.

The huge damage to the seabed caused by the Magnitude 7.8 quake meant the closures could be extended further, Guy said today.

The Government will also spent $2 million investigating the impact of the quake on the fish stocks.

Guy said between 50 to 75 per cent of paua stocks were rotting after the seabed rose up to four metres in places. The species could take a decade to recover, he said.

As a result, the $2m paua fishery will be closed for at least three months. The $23m crayfish fishery, which fared better in the quake, will only be closed for a month, allowing fishers to resume their work ahead of the lucrative Chinese New Year celebrations.

Around 200 people were employed in the local fishing industry and job losses were likely, Guy said.

The fishing companies would not be compensated for their losses. But some could be eligible for relief announced by the Government last week.