"Swells can cause surface flooding and debris wash up including driftwood, seaweed, sand and gravel."
Both the Interislander and Bluebridge ferries have warnings on their websites saying sailings may be affected today and tomorrow – and the Interislander is warning its customers that if sailings do go ahead, they will be "unpleasant".
It comes amid a week of wild weather for the country.
A complex low developed over the North Island yesterday and is expected to move up the country eastwards today and tomorrow.
Heavy rain watches are in place for some North Island areas including Northland, Bay of Plenty and Taranaki, meanwhile, heavy rain is easing over recently affected South Island areas.
The Lindis Pass, SH8, between Tarras and Omarama, remained closed overnight with fresh snow falling and several areas of slips and flooding, said Waka Kotahi NZ Transport Agency.
Group controller for Canterbury CDEM Sean Poff said local councils and emergency management staff are responding to flooding and wind issues in their communities.
"The Canterbury Emergency Coordination Centre remains activated to coordinate across the region."