A man was rescued by Nelson surf lifesaving crews after flooding trapped him in his house bus in a night of heavy rain for parts of central New Zealand.

At least three people got stuck in vehicles after the Tasman region was hit by a deluge overnight.

In the most dramatic rescue a small house bus became stranded in a flooded river near Bartlett Rd quarry, Hope, in Tasman about 1.40am.

The middle-aged man was saved from the rising water by a crew of surf lifesavers in their boat at 3am.

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Crewman Noah Hosie said when they arrived the bus was about 25m out from the river's high tide mark.

"That would be the normal riverbed and the river has come up and around him."

He wasn't sure why the man, a Kiwi, had become trapped, but assumed the river had flooded due to heavy rain in the area during the previous 24 hours.

The water had crept into the floorboards of the bus by the time they arrived.

The man, who also had his own lifejacket, opened a back door of the bus before climbing into the boat.

Hosie said the man seemed to be okay but appeared more worried about what would happen to his bus.

"He wasn't cold because he was nice and dry in his bus."

Hosie said the man made the right decision by calling emergency services as the river was heavily swollen with a strong current.

Police said two more motorists also had to be rescued from their vehicles this morning after they drove into floodwater outside Blenheim.

Police said a vehicle briefly got stuck in water on State Highway 6 near Kaituna about 5.10am before the driver was helped to safety. Another car became stuck in water on Waimea West Rd near Brightwater.

Significant flooding has also been reported on SH6 near Renwick, outside Blenheim.

Rain brought down a slip that is now blocking part of the Kohatu-Kawatiri Highway at Glenhope.

The wet weather had also led to problems for the capital's commuters after a train station flooded and a harbour ferry service was cancelled.

MetService forecaster Tom Adams said a large amount of rain had fallen over central regions in the past 12 hours.

Some of the most intense rain had been around Takaka Hill, where 22.2mm fell in one hour last night.

Adams said the worst of the rain was over, but there would still be heavy showers across the country today and wild winds for the next few days.

A southerly change would also bring snow. Freezing levels are getting lower by the hour.

Snow was now forecast to fall down to 400m in the far south.

Adams warned many of the South Island's high passes would be affected in coming days.