Sunday's Interislander services have been cancelled after monster waves averaging 6m were recorded in the Cook Strait.
MetService forecaster Tom Adams says at 5:30am on Sunday an ocean swell measuring 11.4m was recorded. The average single-storey house is 4.5 metres high.
The Interislander's website says they've cancelled the trips for Sunday and will only sail if conditions permit.
Mr Adams says there's potential waves will get up onto the roads along the south coast, especially around high tide from 12-1pm.
"They probably won't cause much damage, but there could be some seaweed on the roads."
Howling westerlies have also caused rough seas down south.
The Southern Ocean wave buoy, near Campbell Island, measured a 19.4m wave on Saturday morning.
It's the largest wave ever recorded in the southern hemisphere, but Mr Adams says since the buoy was only installed six months ago it's likely there have been others of similar size before.