A state of emergency has been declared for Auckland.

Heavy rain is causing havoc in Auckland and Northland as more warnings are issued and people are being warned to prepare for evacuations.

Auckland mayor Wayne Brown has confirmed to RNZ that he has declared a state of emergency and has delegated powers to his deputy, Desley Simpson.

Auckland Transport says surface flooding is widespread in parts of West Auckland and is urging people to stay clear of floodwaters.

Several schools have also been evacuated in the region.

And an emergency alert has been sent out: "Heavy rain and thunderstorms are affecting the Auckland region and expected to continue into the evening, potentially through to midnight tonight," it said.

It warned to call 111 if life or property was at risk, and to seek shelter with friends and family if you needed to evacuate.

Heavy rain warnings are in place for Northland, Auckland, Coromandel Peninsula, Bay of Plenty including Rotorua and in the South Island for Nelson/Tasman south of Motueka, Marlborough about and north of Awatere Valley and the Grey and Westland districts from Fox Glacier township northward.

Meanwhile, the government will step up support for those affected by flooding in Auckland following Auckland Council declaring a local state of emergency.

'NEMA's National Coordination Centre has been activated and the Government stands ready to provide any support that is needed,” says Minister for Emergency Management Kieran McAnulty.

'NEMA have been closely monitoring throughout the course of this event and keeping me up to date. This declaration gives us the ability to coordinate further resources for affected areas.

'I urge people in Auckland to check Auckland Emergency Management's social media accounts and visit www.aucklandemergencymanagement.org.nz and listen to radio for the latest information. As always, the Government is assisting as much as possible.

'I'd like to acknowledge all the agencies whose staff are working hard to manage the impacts of this server weather. Stay safe and call 111 if you or anyone else is in danger.”

Auckland Emergency Management has opened a Civil Defence Centre to assist those that have been displaced or need assistance following today's severe weather. The centre is open now at Te Manawa Library which is located at 11 Kohuhu Lane, Massey (Westgate).