MetService has issued a heavy rain warning for Nelson through to Mount Taranaki and the Tararua Ranges.
A front that drenched the West Coast over the past few days is now heading north.
Heavy rains began in Nelson and western Marlborough on Monday night and will continue through till Tuesday evening. Up to 200mm is possible.
About 250mm of rain is expected to fall in higher parts of Mt Taranaki until Wednesday.
Moderate rainfalls about the Tararua Range and northern hills of Wellington may become heavy and possibly thundery on Tuesday afternoon.
Old Waimakariri Bridge closed
A bridge north of Christchurch will be closed for much of the day due to concerns over high flow levels.
Christchurch City Council says it closed the Old Waimakariri bridge on Main North Road after heavy rain upstream.
Detours are in place. The closure does not affect the main Waimakariri Bridge on State Highway 1.
An intense downpour lasting about 90 minutes caused knee-deep flooding at seven houses in Murray Street, Greymouth, on Monday.
Flood waters also flowed through several shops and Revington's Hotel in the business district.