Coastal residents in Porirua and Kapiti are being urged to batten down the hatches - with heavy swells forecast for 24 hours from midnight tonight

The regional Emergency Management Office's Jeremy Holmes says they're expecting surface flooding, overflowing streams, and debris displacement.

He says waves could top four and a half metres early tomorrow, and the next 12 to 24 hours will be pretty rough time.

Earlier this afternoon a tornado tore through an area of the Kapiti Coast.