Weather experts are forecasting major swells of up to six metres to slam Wellington's south coast from early Tuesday morning.

MetService has issued a Heavy Swell Warning for 41 hours between 6am Tuesday and 11pm Wednesday.

It covers the coastline between Sinclair Head and Baring Head.

In April last year, five homes had to be evacuated after six metre waves flooded roads and front yards between Owhiro and Breaker Bay.

One person was knocked over by the waves and had to be taken to hospital with moderate injuries.

Owhiro Bay Residents Association spokesman Eugene Doyle said they know the swells this time will have a lot of power.

"They're big waves with long intervals. That means there's about 15 seconds between them, so they can gather up water and really deliver a big punch."

Doyle said people need to take care with their loose items.

"You don't want a car, or a big log, or something like that in front of your house, that as we found [out] last year can come crashing through it."

After last year's damage a new alert system was set-up to warn residents in advance of similar waves and give them time to prepare.

But Doyle said nobody in their community received an alert on Sunday when MetService issued its warning.

"Good warnings and clear advice are absolutely critical in these situations, and I just think the city and the region aren't operating quite at the level we need them to be at the moment."

The Wellington Region Emergency Management Office said it was aware of some technical issues with the alert system, and that MetService was looking into it.

It said a meeting was being held at 11am to discuss the potential impact of the swells, and residents can expect updated advice to be available around midday.

Metservice is expected to release an update on the swell warning at 2pm today.

It has been approached for comment as to why no alert was issued.