Those hoping to cross the Cook Strait by ferry today are being told not to panic after comparisons with the storm that sank the Wahine.

Cyclone Cook is expected to bring a weather system with the same intensity as the 1968 storm that sank the Wahine ferry.

Cook is regarded as the worst storm New Zealand has seen in generations, bringing predicted winds of more than 165km/h and towering waves.

But KiwiRail network services group manager Todd Moyle said the weather may be similar to 50 years ago, but ferry safety has changed.

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"We have pretty strict protocols about when we do and don't operate, and we'll be monitoring the weather and making pretty strict assessments on that.

"If the weather does get worse, we'll make the call on whether or not to operate that ferry.

"It's significantly different now to what it was then, and I think weather forecasting and monitoring is better than what it was.

"That enables us to make much better decisions on when we don't operate services."

For now, ferries are sailing.

Interislander passengers are being told to keep an eye on the website, as any cancellations will be announced there first.

Wellington Region Emergency Management Office regional manager Bruce Pepperell said the storm would move down to the lower North Island by this evening, which was good timing.

"It'll be largely overnight, and everyone generally will be at home, in their beds.

"That's probably the best place for them."

He said the usual safety messages applied, such as cleaning out any gutters and drains, and tying down outdoor furniture.

Because of the unpredictable nature of cyclones, in intensity and the path they would take, he warned New Zealanders to prepare for the worst.

"Anybody who's travelling should take notice of what's happening in the area they're going to.

"Check the Civil Defence postings for where you're going, stay out of trouble spots.

"It's probably not a good idea to go camping on the beach in the Coromandel, for instance."

Winds are expected pick up in Wairarapa and Wellington overnight, and possibly in eastern Manawatu, Horowhenua and Kapiti.

MetService meteorologist Andy Best said he'd never seen a storm like Cook.

He said the last one to have similar conditions was Cyclone Giselle, which hit New Zealand in 1968 and contributed to the Wahine disaster.

The sinking of the Lyttelton-Wellington ferry Wahine on April 10, 1968, was New Zealand's worst modern maritime disaster, claiming more than 52 lives.