About 1300 homes and businesses in Auckland's tornado-devastated Upper Waitemata Harbour remained without power last night while air passengers were stranded around New Zealand because of cancellations and delays.

Powerlines company Vector said repair crews were hampered by traffic congestion and extensive damage to roads and properties in their efforts to replace equipment knocked out by the swarm of tornadoes which swept through northwest Auckland.

Spokeswoman Sandy Hodge said eight power poles and three transformers needed replacing around the Herald Island residential enclave north of Hobsonville and about 780 customers supplied from that part of the network would "unfortunately be affected by an extended outage".

"Due to the nature of the damage, alternative generation of supply is not an option," she said.


She was unable to estimate how long they would have to rough it without power, but recommended that those dependent on electrical medical equipment make alternative arrangements or alert emergency services.

Hundreds of other people around Hobsonville and Whenuapai also remained without power last night, with restoration efforts complicated by a need to ensure properties seriously damaged by the tornadoes were not given their electricity back prematurely for safety reasons.

Ms Hodge said power was knocked out to about 1800 properties initially including 48 affected by a lightning strike in Henderson, although their supply was restored relatively fast, as was that of about 450 others.

The Transport Agency closed the Hobsonville Motorway on State Highway 18 west of Greenhithe for more than two hours until about 4.15pm, after winds brought down light poles, destroyed some of the new road's orange noise walls, disabled traffic cameras and scattered debris.

Thousands of air passengers were stranded at Auckland Airport and elsewhere after more than 40 flights were cancelled or delayed, and incoming aircraft were diverted to other centres.

One man called the Herald from Nelson after his evening flight to Auckland was cancelled and Air New Zealand told him there was no alternative seat available until 1.20pm today. He was annoyed the airline had not offered him accommodation.

Although Auckland Airport lifted operating restrictions at 5.50pm, after almost four hours of disruption, airlines were left with a serious backlog of flights to clear.