A state of emergency has been declared in the Nelson Tasman region after heavy rain continued unabated this evening.
Tasman Mayor Richard Kempthorne made the call because the saturated ground had increased the risk of slips throughout the region.
The rain has already caused flooding and slips in many areas.
The declaration gives Civil Defence the power to requisition extra resources and police additional powers including evacuation.
The declaration remains in force for seven days unless lifted earlier.
Emergency services had been strained and group controller Jim Frater consulted them, both regional mayors, the Golden Bay Civil Defence controller and Civil Defence Ministry before recommending the declaration being made.
Nelson city and eastern Golden Bay were most affected by flooding and slips at this point but roads all over the region were closed, Civil Defence said in a statement.
People were warned to keep away from swollen rivers and other flood-affected areas.
The heavy rain was expected to continue until noon tomorrow.
Earler today, a motorist narrowly escaped plunging into the sea when his car was hit by a falling rock dislodged by a downpour in Nelson, a witness says.
Metservice has issued severe weather warnings for much of the North and South Islands.
Nelson has been hit hard by heavy rain, with several roads closed due to flooding and council workers setting up sandbags to prevent it spreading.
Lawyer Rick Farr said the treacherous conditions had dislodged debris above the coastal Rocks Rd.
He watched as a rock "half the size of a car'' slammed into the side of the four wheel drive just metres ahead of him in a queue of traffic.
Its driver was "extremely lucky'' not to have been pushed into the sea or crushed by the debris, Mr Farr said.
"There was just an explosion from the side of the hill and suddenly we can see very large boulders heading towards us.
"It was a split second and stuff came right at this guy's truck and slammed into the side of him and then stopped.
It's remarkable he wasn't pushed over ... He's the luckiest man alive.''
The driver appeared unhurt as he pulled his car over to the side of the road to check for damage, Mr Farr said.
He said Rocks Rd was prone to erosion and was dangerous in wet weather.
"They need to do something about it or someone's going to be killed one day.''
MetService said significant rain was expected to hit many areas across New Zealand in the coming days as an active front moves eastward across the Tasman Sea.
Most of the country was forecast to receive showers today, with the heaviest rain expected in west and north of both islands.
MetService says warning amounts of rain are likely today and early tomorrow for Westland and Buller, Marlborough, and for Nelson where as much as 400mm of rain may fall about the northwest ranges.
Nelson City Council earlier said it was laying precautionary sandbags in areas that could be affected if the Maitai River continues to rise.
The council said several roads had been closed as a result of surface flooding due to the Maitai River rising.
