Wellington's south coast is being battered by waves of up to 11 metres.
MetService put out wave warnings yesterday for the area.
Duty forecaster William Nepe said the waves were big enough to stop ferries crossing the Cook Strait.
He said a wave rider on the south coast is measuring six metre waves, which occasionally are reaching nine or even 11 metres.
For comparison, four-metre waves are considered heavy, he said. Areas such as Marine Drive are likely to be affected.
Nepe said the large waves were forecast to hit the east coast of the North Island and are probably already there.
A central fire communications staff member said there had not been any weather-related calls from the area this morning.
A spokeswoman for KiwiRail, which owns the Interislander ferry, said sailings were cancelled through to late afternoon today due to rough weather on the Cook Strait.
It is hoped the ferry will sail tonight if swells reduce as forecast, she said.
Any updates will be available on the Interislander website.
"We expect to have a further update on the situation this morning. We regret any inconvenience to our customers but safety is always our first priority."
The Beach House and Kiosk waiter Andrew Redyk said there were spectacular, large swells.
He said they are three times bigger than normal.
Redyk said there are a lot of rocks stopping the swells getting to the road so the cafe is open as normal.
He said normally there are a lot of people out on the water but today there's no one.