The Marlborough District Council continues to keep a close eye on the Wairau River, which is expected to peak at midnight.
Civil Defence remains on standby as heavy rain has closed roads and cut off some isolated areas to the north and west of the region.
The council's assets and services manager Mark Wheeler doesn't expect the Wairau River will burst its banks and describes the flooding as a one in seven year event.
He says the council's flood control system should be able to cope, and floodgates and stopbanks on the river are being monitored regularly.
"It's well stock banked and we're not too concerned but ... we've just got to have people out keeping an eye on that all the systems are operating, that flood banks remain closed, and flood banks don't get breached and that sort of thing".
Close to record rainfall on West Coast
Rainfalls on the West Coast have been close to record levels this weekend.
More than 400 millimetres of rain fell over a 36 hour period in some areas, causing the Buller River to rise rapidly and flood much of the surrounding farmland.
MetService forecaster Allister Gorman says the majority of rain has passed over the South Island and is now heading towards the central North Island.
He says in the Westland area at the back of Hokitika there is been about 480mm of rain over the last two or three days and at the back of the Westport area there has been just under 400mm.
Mr Gorman says the rain on the coast has been almost as heavy as in the ranges, which is unusual.
Nelson Tasman Civil Defence says State Highway 65 between Murchison and Springs Junction will remain closed overnight because of slips brought down by flooding.
The Wairau Bar Road just past Spring Creek's Ferry Bridge will also remain closed while the Wairau River continues to rise.
But some roads which were closed during the day have reopened.
Traffic is flowing again on State Highway 6 between Havelock and Rai Valley.
Also open, the Takaka-Collingwood Highway at the Waitapu Bridge and Maitai Valley Road at Sharlands Creek in Nelson.
Avon Terrace from Bridge Street to Hardy Street in Nelson is expected to reopen on Monday morning.
Westport no longer cut off
Flooding that cut off Westport is beginning to recede, and the part of State Highway 6 between the town and Greymouth has reopened after being shut for most of Sunday.
Flooding from the Buller River had closed roads around Westport for much of Sunday day.
Buller District mayor Pat McManus says the river rose rapidly and caught out some farmers, who had not moved stock.
But he says he drove down the main street of Westport late on Sunday afternoon and expects the town to be fully operational on Monday.
Mr McManus says there's surface flooding in some low lying areas of Westport and the flooding is the worst the town has seen since about 1970.
Police earlier said they knew of only one resident who had been evacuated, from a property between Carters Beach and Westport.
Heavy rainfall caused minor flooding in Murchison, Nelson and Golden Bay.
The Takaka River in Golden Bay rose over the Waitapu Bridge, closing the Takaka-Collingwood highway at that point.
In Murchison, Neds Creek overflowed into five properties, four of which have flooding though garages or sleepouts. One property was sandbagged.
A small civil defence team from the Blenheim Volunteer Fire Brigade is based at Canvastown, and is watching the water levels there.