Authorities in New Zealand are evacuating several areas of the capital city after declaring a state of emergency over a “significant swell” that is expected to batter the coastline this week.

A mandatory evacuation order will take effect at 9am local time on Tuesday for waterfront properties in southern Wellington suburbs like Owhiro Bay, Island Bay, Houghton Bay, and Breaker Bay.

The order is expected to remain in force until Wednesday.

Authorities said the measure was necessary because of a “significant swell” forecast to hit the region. Emergency management spokesperson Dan Neely warned people to avoid beaches and coastal areas.

“In 2020, a heavy swell event struck Wellington’s southern coast with 5.5m waves pounding coastal suburbs, causing widespread damage and evacuations. Tomorrow we expect the swells could be up to 8m around Wellington’s south coast, so we are preparing for a significant swell event and asking the public to do the same,” he said.

“The sun might be shining, but the swells could bring debris and surface flooding to roads, especially around high tide at midday. The public is urged to avoid Wellington’s south coast roads as well as coastal roads around Wairarapa. Extreme caution should be taken if you have to drive on these roads.”

The national weather agency, MetService, warned that waves could reach up to 8m along Wellington’s coast and as high as 10m in neighbouring Wairarapa.

Forecasters described the conditions as rare and potentially dangerous. “It’s definitely a significant swell event,” meteorologist Devlin Lynden told Newstalk ZB.

“We do occasionally see these heavy swell events but this one is particularly notable.”

The large waves are being driven by strong winds associated with a fast-moving weather system in the southwest of the country.

Authorities warned of possible coastal flooding and urged residents to follow official advice and stay away from exposed shorelines.

Wellington City Council is advising affected residents to “prepare a bag with essential items such as medications, important documents, personal items and clothing, prepare to take pets and their supplies with you, organise to stay with friends or family” and to “check on neighbours and anyone who may need help”.

The severe marine conditions are also disrupting transport across Cook Strait, the stretch of water separating New Zealand’s North and South Islands.

Ferry operators Interislander and Bluebridge cancelled sailings scheduled for Tuesday while Bluebridge also called off one service on Monday evening.

Authorities continue to monitor conditions and are advising residents in vulnerable coastal areas to stay updated as the weather system approaches.

“Tomorrow won’t be a good day to go out on any sort of southern coastlines, especially around Wellington,” meteorologist Lewis Ferris advised residents.

“Don’t take the dog for a walk, don’t go just to see the large waves roll in.”

Wellington civil defence controller Phil Becker said the forecast conditions posed a serious threat.

“The size of the forecast waves means there is a real risk to the safety of residents on the coast and that properties may be inundated by seawater.”

MetService said hazardous swells were also expected to impact eastern New Zealand. “A powerful southerly swell is expected to affect eastern coastlines from Otago to Gisborne through to midweek, bringing large waves and dangerous coastal conditions,” it said.

“These long-period swells carry significant energy, allowing waves to surge further up beaches, over coastal roads, and into low-lying coastal areas than usual.”