The Grey District Council, located on the South Island's West Coast, is providing sandbags to "anyone in need".
"If you’re concerned about flooding, please feel free to come by and pick them up," a post on social media read.
"Stay safe and prepared."
State Highway 6 between Haast and Lake Moeraki is set to be closed overnight due to forecast "severe weather conditions".
The road will close from 7 pm tonight and reopen at 8 am on Friday subject to inspections.
Meanwhile, heavier rain in the upper North Island is tipped to ease before midday on Friday, though it will linger further east.
MetService has warned Auckland and Northland commuters heavy rain on Friday morning could lead to "wet roads and slower traffic".
It comes as the forecaster earlier said the main rain band of the large weather system is expected to extend into the North Island from late Thursday into Friday.
"The heaviest rain is expected overnight in Northland and Friday morning around commute time for Auckland, extending to other areas throughout the day.
"Allow extra travel time, drive to the conditions, and don’t forget your umbrella," MetService said.
MetService says areas in the South Island have recorded over 100mm of rain since midnight.
The Paradise Peak weather station in Tasman recorded 113mm of rain between 12.01 am and 1 pm on Thursday.
This was followed by:
MetService says "significant amounts" of rainfall has been observed in western regions of the South Island, with "plenty more to come" for the country in the next 24 hours.
"The top of the North Island is set to see impressive amounts throughout the day as well and [rainfall] is projected to spread eastwards."
A Westland trail has been forced to close after it was flooded out during the deluge.
The Weirs are flooded and “impassable” according to the West Coast Wildness Trail.
“Please be aware there may be issues in other places. Please take care in all places while on the trail.”
The Tasman District Council's warning residents to remain alert for flooding along major rivers as tides peak late Thursday evening north of Motueka, and Friday evening in Nelson.
Up to 400mm of rain is expected in the area on top of what has already fallen, bringing the expected total to about 550mm.
The council said the heaviest rainfall is expected at the end of the weather event when the ground will already be saturated, increasing the risk of flooding.
The council said there's also a possibility rain amounts could increase and warnings over the area could extend.