UPDATED 6.21pm: Heavy downpours continue to pelt Waikato, Auckland, Waikato, Waitomo and the Coromandel.

The Fire Service said Riverview Road in Huntly is under a foot of water and half the road is blocked by major slips.

It said it's also getting reports of houses being flooded on both sides of the Waikato River in Huntly.

And only one lane is open on Waiwera Road north of Auckland, after a slip which has disrupted traffic. 

It's the remnants of the storm that plunged South Australia into darkness and has been hammering the North Island with reports of flooding, slips and power outages throughout the day.

Weatherwatch analyst Phillip Duncan said more rain should be expected throughout the evening and there could more patches of flooding. 

In Auckland, rain and thunderstorms have caused some surface flooding and power outages.

The Fire Service said the worst hit area was East Coast Bays where about 15 homes were affected by flooding this morning.

Power company Vector said unconfirmed lightning strikes caused multiple outages around Torbay but power had been restored as had cuts in New Lynn.

There was an emergency power shutdown in Rothesay Bay for repairs to be made to the network.

Other North Island areas, including Bay of Plenty, Coromandel Peninsula, East Cape and Central Plateau also face a drenching.

NZTA said there were several small slips on SH25 between Thames and Coromandel but all were passable.

The MetService earlier said a front moving eastwards across New Zealand on Sunday would bring rain to Northland, Auckland, Waikato, Waitomo, Coromandel Peninsula and Bay of Plenty.

Many of these regions were saturated during recent days, so surface flooding and slips were possible.