Wellington's Mayor says people need to be prepared for the weather to get worse

Swells are expected to become extreme along the South Coast this evening, with Breaker Bay forecast to take the brunt about 9pm.

Residents on Breaker Bay road between numbers 34 and 194 are being urgently evacuated.

A local state of emergency has been declared.

Wellington Mayor Andy Foster says things could get far bigger than six metres.

He says they're expecting up to eight metres and some parts of the coast are particularly vulnerable which could see up to 1 metre and half of waves hitting dwellings.