New Zealand Transport Agency regional performance manager Mark Owen told Newstalk ZB getting SH7 in the Lewis Pass - now the main transport link between Picton and Christchurch since November's big earthquake - open was a priority.

The central South Island highway is among several closed by the weather bomb.

Along with Lewis Pass, other South Island highways closed by slips and fallen trees are SH73 Arthur's Pass between Christchurch and Greymouth and SH65 between Murchison and Westport.

"So it's pretty difficult getting north and south on the top of the South Island, due to the impacts of this weather event. The main thing is with SH1 closed north of Kaikoura we know the inland Lewis Pass-Murchison route is critical particularly for freight and for people getting to the ... [interisland] ferry.

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"So that's where our focus will be, trying to get that Lewis Pass open. It just depends on the nature of the slips and the amount of flooding and debris we have to get rid of."

West Coast Regional Council chief executive Mike Meehan told Newstalk ZB they had fared better than expected, but were still keeping an eye on the Grey and Buller rivers.

The front had moved through the Westland and Grey districts and was now passing through Buller towards Nelson.

"Rivers have gone through their first alarm levels, but down in Franz Jozef and Hokitika through the night it wasn't the flooding that we thought there potentially would be. That's a good thing."

The focus remained on the Grey and Buller rivers. Meetings were held at 12.30am and 5.30am, and plans were being followed to monitor the situation.

"They're very big catchments and they've got a lot of tributaries that run into them, [and] that have significant flows. So we're just keeping an eye, but we've got got good systems in place to [do that]."

In the North Island, SH2 between Wellington and Wairarapa, over the Rimutaka Hill, is closed because of high winds, Owen said.

"We're monitoring that ... when the wind drops we'll look to open."

He warned motorists to watch their following distances, and take care when coming around corners, in case they came across slips or debris. Roads would be slippery, even after the clean-up.

High winds were also having a big impact on a wide area.

"[I'd] advise people to take extra care, particularly high-sided vehicles and motorcyclists. who are very vulnerable in these strong wind gusts that are happening at the moment. [People] just need to be mindful that this is quite a significant weather event."