New Zealand officials have declared a state of emergency as the biggest downpour on record has caused flooding and traffic chaos on New Zealand's North Island.

Cars became submerged and were witnessed floating down Auckland's major roads - some commuters choosing to disembark buses stuck in traffic jams to run for their lives as waters rose on the Northern Motorway.

Residents in the West Auckland suburb of Henderson battled through the rising floodwaters to meet with rescuers and first responders.