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Massive 15-metre waves are expected to hit parts of the South Island, as rough wintry conditions head towards the country today.
Civil Defence says it is expecting potentially hazardous king tides and high seas on the West Coast from today until next Tuesday.
WeatherWatch says a Southern Ocean storm is "pouncing'' the area - bringing waves of up to 15m high to the south west, as well as heavy snow, hail, isolated thunder and severe gales.
"The rough West Coast lives up to its name with highly dangerous beach and marine conditions across the next 72 hours at least,'' a statement said just before 8.30am.
Boaties and anyone keen on fishing on the rocks are being told to stay home until at least Tuesday because conditions are too dangerous.
Civil Defence said it would be closely monitoring the situation, but people should be aware of the threat.
West Coast Emergency Management director Mark Crowe said low-lying areas along the coast could be at particular risk.
"It's a combination of some reasonable king tides, which we were notified about a month ago, then there's obviously the swells that come through with it and the gale force winds as well," he said.
"So we really just wanted to communicate that combination of factors and just heighten people's awareness."
Meanwhile, several streets in eastern Christchurch, including Anzac Drive, Wainoni Road in Aranui, and New Brighton Road, flooded yesterday due to high tides and river levels.
The city's Transport Operations Centre is urging drivers to slow down while driving through floodwaters.