The storm is causing disruption to road and rail links in the upper South Island.
State Highway One is closed from Ward near Cape Campbell to Saltwater Creek near Sefton.
The line between Picton - Christchurch line is closed due to slips, flooding and debris.
However, Cook Strait ferries are still sailing.
South of Christchurch, SH1 is closed from Rakaia to Ashburton. Parts of the inland highway are also closed.
Emergency services say there are numerous reports of flooding.
Police say the worst affected areas include Amberley, Leithfield and Rangiora.
At Sefton, 12 residents were evacuated to the local school hall.
State of emergency
Civil Defence says a state of emergency will remain in place for the Marlborough region until at least Thursday afternoon.
An emergency was declared by the Marlborough District Council on Wednesday afternoon.
Civil Defence Controller Mark Wheeler, told Morning Report it was done to enable police to force unwilling residents to leave their homes.
Some 35 people in Picton were evacuated on Wednesday night from a camping ground and from houses near a flooded creek.
They spent the night in the auditorium of Queen Charlotte College. Red Cross volunteer Sam Morrison told Morning Report their morale is good.
Checks will be made at first light for flooding and fallen trees in the town.