Heavy rain from Cyclone Gabrielle is likely to arrive in Northland slightly earlier than expected, while the Auckland Harbour Bridge is already under a wind warning.

An orange warning is in place for severe wind and heavy rain for several areas including Northland, Auckland north of Whangaparaoa and Great Barrier Island.

MetService says regardless of the storm's eventual track, there is a very high risk of extreme and impactful weather over the upper North Island late Saturday night, spreading to south and central New Zealand by Monday.

North of New Zealand, Norfolk Island has declared a red alert and residents have been urged to take shelter as Tropical Cyclone Gabrielle continues to track straight towards the island.

The Bureau of Meteorology says gale-force winds could impact the island through Saturday night and into Sunday.

Emergency Management Norfolk Island (EMNI) moved the island to a red alert Saturday afternoon, meaning people should stay inside until further notice.

Strong winds are already being felt in the north, with Waka Kotahi issuing a strong winds warning late this afternoon for the Auckland Harbour bridge.

"Please take extra care especially if you are in a lighter or high-sided vehicle or riding a motorcycle."

A red warning for heavy rain was issued today for the Coromandel Peninsula and Tairawhiti Gisborne north of Tolaga Bay.

MetService says it expects up to 400 millimetres of rain to fall in the regions, mostly on Monday.

The storm is due to track across Northland before moving south to Auckland, Coromandel, Waikato, Bay of Plenty and Gisborne on Monday and Tuesday.

Forecasters are warning of strong wind, heavy rain and big seas.

MetService meteorologist Lewis Ferris said the cyclone would bring widespread severe weather.

The cyclone had taken a more eastern track over the last few days, but there was still disagreement over where the central point will lie when it made landfall, Ferris said.

"It's still looking like Monday-Tuesday are going to be the biggest days for the weather with the approaching cyclone. The worst impacts, where they are and when they occur, are still going to be riding on where the track of the cyclone actually eventuates."

The storm is due to track across Northland on Sunday before moving south to Auckland, Coromandel, Waikato, Bay of Plenty and Gisborne on Monday and Tuesday. It is possible that even Wellington could see some impacts, MetService said.

It has been upgraded to category 3.

MetService has issued heavy rain and strong wind watches ahead of its arrival.

Civil Defence Controller for the Coromandel Garry Towler says as well as heavy rain, winds of up to 130 kilometers an hour are expected and after weeks of severe weather, civil defence officials are very worried.

He said the Coromandel was in a fragile state and Civil Defence was deploying as many resources onto the Coromandel as they could.

He said a mobile alert will be issued this afternoon, and warnings will go out to people in vulnerable areas.

Travel warnings issued

Meanwhile, the government is urging people to avoid non-essential travel in areas that could be hit by Cyclone Gabrielle.

Air New Zealand has cancelled several flights.

Emergency Management Minister Kieran McAnulty said safety trumped the disappointment of scrapping weekend plans.

"We would urge people, despite the inconvenience this would naturally cause, to heed that advice, because it is not given lightly. We are taking this very seriously. Depending on how this tracks it could be quite severe and we're just asking people to take it seriously."

McAnulty said he had assurances government agencies and local civil defence services would update their social media channels regularly.

People were also being urged to stock three days' worth of food and water and prepare for possible power outages.

Supermarkets have urged shoppers to be patient as people stocked up on essential supplies.

St John Ambulance said it was scaling up in preparation for Cyclone Gabrielle.

Spokesperson Dan Ohs said St John had increased deployments in Northland, Coromandel, Auckland, and Bay of Plenty.

There would be extra ambulances and four wheel drives on the ground, he said.

"For us it looks like additional ambulances where that's relevant and in particular, four-wheel-drives. We're also in discussion with Wellington Free (Ambulance). Wellington Free have a rescue unit capability and four-wheel-drive resources."

Parents in Auckland are likely to receive communication from their children's school this weekend about Cyclone Gabrielle.

Yesterday, the Ministry of Education advised Auckland schools that they must decide individually whether to stay open or close in response to the storm. The decision would be based on schools' assessment of health and safety risk of their situation.