Labour Day motorists are being urged to exercise caution and expect delays as they return home from the long weekend.

National road policing manager Superintendent Carey Griffiths said despite the Labour Weekend road toll currently sitting at triple that of last year, he was happy with drivers' behaviour.

"Driver behaviour overall's been good. What disappoints me is having three fatalities."

Mr Griffiths said congestion was most prevalent on main arterial routes heading into city centres, particularly heading south from the Desert Road into Wellington.

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Inspector Willy Taylor of police northern communications said traffic into Auckland from the north was "a slow crawl back to the city" and traffic flows returning to Auckland from the south were medium to heavy.

A power outage in Warkworth added to the congestion for motorists returning to Auckland this afternoon.

A Vector feeder problem knocked out traffic lights on State Highway 1 and disrupted power to more than 400 properties.

New Zealand Transport Agency northern spokesman Ewart Barnsley said police and contractors were directing traffic, and drivers were advised to use an alternate route via SH16.

A generator was being arranged to restore power to the traffic lights and the outage was expected to be resolved by 7pm.

Mr Barnsley said there was also typical traffic congestion around Thames as those returning from the Coromandel squeezed onto the highway system.

There were also delays on the main southbound highway to Wellington, from Otaki to Levin, Sergeant Andy Dow of police central communications said.

Drivers were advised to take extra care, drive to the conditions, take regular breaks "and everyone will get home safely hopefully".

Inspector Rick Jury of police southern communications said there were no major delays heading in and out of Christchurch and despite a few minor crashes, motorists had been well behaved.

Wet weather was also in store for many drivers.

MetService duty forecaster Philippa Murdoch said a rain band was currently moving up the country through Waikato and into Auckland.

"We're expecting that to spread through. There's some scattered rain already through Waikato and we're expecting that to get a bit heavier for a time as it moves through this evening and then easing off overnight."

Another rain band was forecast to move in from the west of the country tomorrow which would bring rain and heavy falls during the evening, Ms Murdoch said.

Mr Griffiths appealed for motorists to be patient, slow down, watch their following distances, expect delays and take care in bad weather.

"We're asking people to adopt the four-second rule in following -- give plenty of distance from the car in front."

He also asked for motorists to avoid unnecessary overtaking.

"You often get the high-speed overtakes and that's where things can get ugly for everybody."

Mr Griffiths said a lowered holiday speed threshold had resulted in about 500 fewer deaths and serious injuries over the past five years.

"It's something that the public are accepting. We've run a lowered holiday threshold since 2010 and the overall trend in relation to deaths and injuries is consistently downward.

"The research says if you do it, it contributes to less deaths and serious injuries."