All ferry crossings are cancelled for Wednesday as waves of up to eight metres are expected in the Cook Strait.
Sea conditions are expected to be very poor from Tuesday evening through to Thursday morning.
The Interislander has cancelled around 13 passenger sailings, while five Bluebridge ferries have also been cancelled.
Interislander told Newshub ferry operations are restricted by wave and swell heights.
"We're not allowed to sail above a six-metre swell, and haven't been able to since the Wahine disaster", said Mark Thompson, general manager of operations.
"The conditions are not safe under maritime rules", he said.
"There'll be a build up of swells up the east coast of the South Island and it's where they hit the heads into Wellington Harbour that causes the problem. It wouldn't be a problem if it was coming from the north because the area is sheltered".
The swells are being caused by a deep low off the south of the country.
"This is a really big southerly push from the southern ocean, with large waves expected for the next 24-48 hours", said Metservice meteorologist Rob Kerr.
The last Interislander sailings to cross the Cook Strait will depart from Wellington at 8:30pm on Tuesday evening, and from Picton at 2:30am on Wednesday morning.
Bluebridge has cancelled all passenger services from 8am Wednesday until midday on Thursday, but that is "subject to change".
Both operators said most customers should have been contacted by now and will be re-booked on the first available crossing.
Metservice said big waves are expected up the length of the east coast, and winds up to 100kmh are expected around Banks Peninsula, Clutha, Dunedin and the Port Hills in Christchurch.
Metservice has issued severe weather warnings for Wednesday with strong winds expected in coastal areas including parts of Southland, Clutha, Dunedin, Banks Peninsula, the Port Hills of Christchurch and Nelson west of Riwaka from Tuesday afternoon until midnight on Wednesday.
There could be severe southwest gales of up to 120 km/h in these areas, as well as in the Wairarapa and the Hawke's Bay until the early hours of Wednesday morning.
Winds of this strength could cause damage to trees, powerlines and unsecured structures and make driving hazardous, especially for tall sided vehicles and motorcycles.
Newshub.
