Dairy farmers who are cut off by road slips in the Tasman district will probably have to dump several days worth of milk.
A Civil Defence state of emergency remains in place in the Nelson and Tasman regions because of flooding due to heavy rain over the past 48 hours.
Collingwood in Golden Bay is unreachable by road due a 50 metre slip at Bird's Hill on State Highway 60, which is expected to take three days to clear.
That means milk tankers won't be able to collect the milk from about 50 dairy farms, west of Takaka.
Federated Farmers says many farms are covered with river silt and debris after more heavy rain overnight, but no stock losses have been reported.
Golden Bay president Graham Ball says farmers are waiting to hear whether Fonterra can collect their milk.
Mr Ball says 580mm rain has fallen on his Golden Bay farm in the past 48 hours.
Rockville farmer Michelle Riley is one of those facing the possibility of having to dump milk.
She farms on a large property with two cowsheds, and says both storage vats are full to the brim at this stage.