"Significant" amounts of rain and severe gales are expected to continue to batter the West Coast today through to Thursday, as emergency services monitor rivers at risk of flooding.
It comes as a front, preceded by strong and moist northerly winds, was forecast to pass through the South Island from the west today, before moving slowly northeast tomorrow, according to MetService.
Central parts of Westland are expected to be hit with a significant amount of rainfall during this period, potentially leading to slips and impassable roads due to heavy flooding.
An orange heavy rain warning is in place for Westland but could be upgraded to a red warning.
MetService this morning updated its forecast to include additional rainfall for Buller. Most of the rain is expected to fall in coastal areas and the Paparoa Ranges, which may affect driving conditions due to surface flooding or slips.
1News weather meteorologist Dan Corbett said Westland has already seen up to 200mm of rainfall but more is expected, with the region potentially seeing 300-400mm over the next 12 to 24 hours.
1News meteorologist Dan Corbett said the region could see "just over half a metre" of rainfall. (Source: 1News)
As the intensity of the weather begins to ease as we head into the weekend, a "new trough" is expected to come in from the far south.
"It'll still be raining, so by the time we're done the rain could be just over half a metre and on the coast, it could easily be 100 to 200mm of rain in places," he said.
"The weather will quieten down as we go beyond Thursday into Friday and Saturday, blustery flow to the south and guess what? There is actually high pressure which is set to build and quieten the weather down for the weekend."
MetService meteorologist Angus Hines told 1News while there are warnings in place for the "broad majority" of the western South Island, the heaviest rainfall is expected in the Southern Alps.
"Our warnings show there could be 500m of rain, maybe more there, in about a 36-hour period," he said.
"It's certainly up here as one of our more significant rain warnings for the year."
Some parts of the Southern Alps have already had more than 150mm of rain as of 1pm today, with "a lot more on the way".
Civil Defence group manager Claire Brown said while the change in the forecast issued by MetService means they "do not anticipate that this will cause major issues, people need to be aware so they can be prepared".
River levels started to come up this morning, with some areas seeing "significant hourly rainfall totals in the early hours of this morning, particularly in the ranges of Westland", West Coast Emergency Management said.
West Coast Regional Council staff are monitoring rivers throughout the West Coast, with short-term protection to be put in place for the Waiho River, at Franz Josef.
The Hokitika River is continuing to rise and will be closely monitored ahead of high tide at 6.45pm.
The Emergency Operations Centre in Westland will activate this afternoon as a precaution to monitor the event over the next 24 hours.
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