Around 13,000 Network Tasman customers were without power overnight, with repair crews beginning restoration efforts this morning.
Civil Defence said this afternoon around 3200 properties were still without power in the Motueka and Golden Bay areas.
Nearly 5000 homes were also without power across Banks Peninsula overnight.
Tapawera was cut off from much of Tasman District because of flooding, and also lost mobile phone coverage.
Reports of lifted roofs, fallen trees and stranded residents were widespread across the district.
All residents connected to a Tasman District Council water supply were urged to conserve water until further notice.
Four Civil Defence Centres have been opened to support those unable to return home, Nelson Tasman Civil Defence has confirmed.
Multiple roads are closed at the top of the South Island and will continue until further notice. This includes State Highway 6 Rocks Rd in Nelson, according to NZTA.
Flooding and slips also caused major disruption on roads across Northland overnight.