People in the low-lying areas of central Whangārei are being asked to move to higher ground on Monday afternoon.
There was a high risk of tidal flooding when high tide hit just before 2pm and possibly a further risk of flooding overnight, Whangārei District Council said on Facebook.
Police and Fire and Emergency have been in the area door-knocking and helping people leave.
The Civil Defence Centre at McKay Stadium, at 97 Western Hills Drive, Kensington, is open for those who need it.
* Cyclone Gabrielle: State of Emergency declared as Northland hit by power outages, road closures
* Chris Hipkins says lessons from January flood have informed Cyclone response
* Cyclone Gabrielle could hammer Coromandel with up to 300mm of rain in 24 hours
The council has shared an indicative map of the flood-prone central district but said people should use their own judgement as well.
“Properties that are on the low-lying coastal fringe are in an elevated stage of danger. If you live somewhere that could be affected by high waves, please consider evacuating to somewhere safe.”
Otherwise, people should conserve water where possible, the district council said.
Meanwhile, nearly 30,000 households were without power in Northland and the Far North amid Cyclone Gabrielle, with people warned they could be without electricity for a week.
Northpower said on Monday morning there were about 18,500 households without power and the company expected that number to grow as the day went on.
Top Energy said 10,500 households were without power in the Far North.
Northpower and Top Energy had been working to restore power where possible but with winds gusting over 140kph, it hadn’t always been safe to do so, Northland Civil Defence reported on Monday morning.
More than 55 of the main high voltage lines had been damaged – about half the network, Northpower said.
“We have not seen this level of damage since Cyclone Bola in 1988,” a spokesperson said.
“Those households affected by an outage will continue to be without power over the coming days, and in some cases a week.”
An image from the Northpower control room showed the extent of damage at 6am Monday. All lines in white, yellow or green were out of action.
“We are continuing to work to make sure things are safe by isolating the electricity supply from the damaged lines. It is not safe or possible to begin to repair most of the issues until the wind abates.”
Some of the damage would require rebuilding and the initial scoping and planning work had already begun, Northpower said.
Many people had also been experiencing a loss of mobile phone services, including internet, phone and text services, the Far North District Council said.
They recommended those without internet connectivity listen to the radio for important updates.
Far North district mayor Moko Tepania told TVNZ’s Breakfast 33 Far North settlements were without power on Monday morning, with only main centres including Kaikohe and Kerikeri unaffected by outages.
In a statement on Monday, Top Energy chief executive Russell Shaw said the network had been extensively damaged and dangerous conditions meant repairs were tricky.
He said those using medical equipment that relied on electricity should tell their retailer if they were without power.
If there was an immediate health threat, people should contact their health provider or call 111.
“Repairs are likely to be complex with multiple faults and damaged equipment,” Shaw said.
“When conditions allow, our focus is on repairing the backbone of the network to get as many people back on as possible.”
Meanwhile, there are seven road closures across the Far North due to fallen trees and one road down to one lane.
At 1pm, SH1 between Brynderwyn and Waipu remained closed due to large slips, with previous detours back in place as of Monday morning.
Light vehicles may detour via Kaiwaka and Mangawhai, while heavy vehicles must detour via SH12/SH14 (via Dargaville).
Further road closures were likely.
In the Kaipara District, a welfare assistance number – 09 439 1111 – had been set up for those affected by the cyclone.
Evacuation centres were also planned at locations across the district and would be advertised if required.