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The MetService has warned of strong winds around Marlborough and Wellington for much of today.
And earlier today, Cook Strait passenger ferry sailings were cancelled as swells of up to 6m were forecast.
Meteorologist Dan Corrigan said the southerlies were bringing heavy swells along the south coast of Wellington.
"We're already observing waves coming over the coastal roads, especially around Ōwhiro Bay," Corrigan said.
"We're seeing surface flooding and debris coming over the roads, so we're recommending that people heed the advice of local authorities and take care around the coast today."
Moa Point Road, alongside Wellington Airport, has been closed after heavy seas threw rocks on to the road.
The road to Eastbourne is also closed until further notice at Point Howard due to debris and heavy seas.
The strongest wind gust was on Banks Peninsula, and was recorded at 133km/h.
Gusts of 93km/h were recorded in Christchurch, and 110km/h in Lyttelton.
The worst of the wind started to ease for Banks Peninsula and Canterbury from 11am, but the gusts continue for Westland and Marlborough.
The southerly swells around Wellington are forecast to ease to 5.5m this evening and 4.5m overnight.
MetService has strong wind watches in place for the lower North Island until 10pm and the Marlborough area until 9pm.
Interislander operations manager Peter Matthews said the company's cancellations today will affect about 1000 passengers.
Bluebridge cancelled its early morning sailings on Thursday and said swells were forecast to worsen today.