Cook Strait ferry crossing 'the roughest yet'

Passengers on the Cook Strait ferry during the southerly storm have called the crossing "the roughest" they have ever experienced.

"This one takes the trophy for the roughest yet," Jeremy Falconer said of his trip on Interislander's Kaiarahi ferry from Picton to Wellington.

"It was difficult moving around the boat due to the movement. Lots of sick people sitting around on the floor and filling the bathrooms."

Another passenger, Nathan Pilcher, said: "Everyone was sitting on the floor, holding on, sitting down with vomit bags and people were lying down in the toilets.

"It was like being on a roller coaster, but you didn't know how big the next [swell] was going to be," he told Fairfax Media.

Pilcher said waves crashed over the top of the viewing deck for about 90 minutes in the open waters of the Cook Strait and one of the ship's ceiling panels was knocked loose.

Interislander ferry sailings have been cancelled after weather in Cook Strait deteriorated earlier than predicted.

Sailings were to stop this evening ahead of the arrival of a large swell.

But KiwiRail's Interislander general manager of operations, Mark Thompson, said 7m waves had arrived earlier than expected.

As a result, the 2.45pm and 5pm sailings from Wellington and the 6.45pm sailing from Picton have been cancelled.

Freight sailings were expected to resume on Friday, from Wellington at 6.30am, and from Picton at 9.05am, depending on weather.

The first passenger sailing from Wellington would leave at 9am and from Picton at 10.55am.

Affected passengers and freight customers would be contacted and rescheduled where possible, he said.

"We regret the inconvenience to our customers. We are always striving to deliver the best possible service, but safety is paramount."

Bluebridge has also cancelled all its sailings between Wednesday night and Friday morning.