Nelson hit by one-in-100 year rainfall, mayor says

The torrential rainfall that has seen Nelson declare a state of emergency has been described as a one-in-100 year event by the city's mayor.

Rachel Reese told 1News it was unexpected as such intense rainfall wasn't predicted for the area.

READ MORE - LIVE: Flooding and evacuations as heavy rain hits parts of NZ

A state of emergency was declared in Nelson after the Maitai River breached its banks, with around 70 homes needing to evacuate.

Reese said there had been good cooperation with evacuations and officials are trying to ensure everyone is out before nightfall.

Video shows the swollen river close to some homes and full of debris.

The situation is unlikely to get any better with up to 400mm of rain still expected to fall until 11pm on Thursday.

Government ministers are set to travel to the area this week to provide support. Damien O'Connor will arrive on Thursday while Kieran McAnulty will arrive on Friday.