Emergency services are rushing to the scene of a serious crash which has closed State Highway 6 between a truck and car in the Tasman District this afternoon.
Police were notified of the crash at 4.13pm today at the intersection of SH6 with Owen Valley East Rd.
The serious crash unit has been sent to the scene, and a rescue helicopter from Nelson is on its way.
No detail on injuries is yet know.
Traffic is also crawling on State Highway 2 towards Tauranga as holidaymakers try to get a head start on their travels.
Traffic was gridlocked Between Te Puna and Bethlehem on SH2 before noon.
A police spokesman said there had been no traffic issues in the wider Bay of Plenty for a couple of hours.
He believed traffic in the area would be the beginning of holiday traffic.
Motorists heading north on Auckland's Southern Motorway experienced delays around the Mt Wellington area after a crash this morning.
A police spokeswoman said it appeared to be a nose-to-tail accident involving three vehicles at the Mt Wellington Highway off-ramp.
Hundreds of thousands of cars are expected on the roads today during one of the busiest travel days of the year.
Nine people died on the roads in the official holiday road toll period last year, and 12 the year before. The period starts at 4pm today and finishes at 6am on Monday, January 13.
Police are set to ramp up their presence on the roads to popular holiday hotspots, and fixed-speed cameras will issue fines to people travelling 4km/h over the limit from this afternoon though the holiday period.
Acting superintendent Amelia Steel said the summer months were a bloody time on the roads.
"These two months, particularly January, [are when] most people die on New Zealand road so we know that we need to be ultra vigilant."
She had a message to drivers.
"Plan the journey, allow plenty of time ... and just stay focused to ensure that your speed is appropriate for the conditions, to ensure that people are wearing their seatbelts in the car, not to drive while impaired - that's either through drink or drugs or being fatigued."
Steel said the best Christmas present she could get would be for travellers to get to their destinations alive and unharmed.
The New Zealand Transport Agency expects heavy traffic to start early today, making traffic jams likely from midday north and south of Auckland.
NZTA has crunched the numbers to work out exactly when the traffic will be heaviest.
The interactive holiday journeys map shows predicted traffic flow across the Christmas/New Year period.
For Aucklanders heading south, the worst bottleneck will be around Takanini and Papakura, while northbound the heaviest traffic will be between Puhoi and Wellsford.
Based on previous years, traffic at both pinch points is expected to start building at 11am, and by 12pm is expected to be at a crawl, only easing after 8pm.
Motorists are advised to leave early this morning or leave the driving until after dark.
But don't wait until tomorrow. Traffic is expected to build on the Southern Motorway from 8am and won't ease until after 6pm, while northbound traffic should ease around 5pm.
If previous years are anything to go by, Sunday's traffic is expected to be much calmer heading south, with only a brief heavy period mid-morning. But northbound traffic will remain heavy from 9am to 5pm Sunday.
While the traffic predictions are based on past data, factors like weather and driver behaviour could change those patterns.
It's hoped the recent widening of State Highway 1 to three lanes each way between each Takanini and Papakura will ease congestion.
For those staying in Auckland tonight, police hope free public transport, and warnings of extensive breath-testing points, will stop people getting tipsy or drunk and then getting behind the wheel.
Public transport will be free from 4pm today under Auckland Transport's Home Free promotion, with customers with HOP cards who tag on after 4pm receiving no charge on their account.
Tāmaki Makaurau road policing manager Inspector Scott Webb urged people to leave their cars at home, saying the initiative would let people enjoy an after-work drink and still get home safely.
Auckland police will also be out in force breath-testing people to make sure they're not tipsy or drunk when they get behind the wheel.
AT staff and police have been conducting checkpoints across the city over the past two weekends. A "disappointingly" high number of people had been caught driving under the influence, police said.
State Highway 1 on the Kāpiti Coast north of Wellington is likely to be bumper to bumper from 9am, and from 6.30am tomorrow.
Wellington spokesman Mark Owen said the heavy traffic on the main highways would last well into next week.
"Next Monday [and] Tuesday will be busy, and then ... Christmas Day, Boxing Day and the day after."
"It's really going to be busy from ... Friday right through until the middle of next week."
He said travellers should use a tool on the agency's website to see when traffic would be lightest.
Delays could continue throughout summer, as double the usual maintenance roadworks are planned throughout the country.
Owen said although people would face delays over the summer months, the maintenance work needed to be done, and it was the best time to do it.
He said the work would be paused from today until January 6 to help ease congestion, but there would still be lower speed limits in place where roadworks had begun.
Levin resident Antony Young said he expected massive queues of motorists today, and likely delays of an hour and a half.
"It seems to be getting progressively worse year after year," Young said.
"This stretch of road has overreached its capacity, our infrastructure is crumbling, our national highway system just is inadequate."
He said he feared for locals' safety.
"We're really worried the state highway goes straight through our town. We have young children and a large elderly community that cross that road every day."
All four lanes of the Longswamp section of the Waikato Expressway will be open to traffic for holiday traffic.
The 5.9km Longswamp section – where State Highway 1 has been widened to four lanes, with side and central safety barriers – links the completed Meremere section in the north at Hampton Downs, to the completed Rangiriri section in the south at the Te Kauwhata interchange.
"We are very pleased to have Longswamp open on all four lanes before Christmas. We still have some final surfacing work to complete early next year but having holiday traffic spread across the new lanes has been a priority," Waka Kotahi NZ Transport Agency Waikato portfolio manager Darryl Coalter said.
Southbound traffic will be at 100km/h, but northbound will have a speed restriction of 70km/h until the final asphalt surfacing is completed in the new year.
Construction started in early 2017, building the southbound lanes first. With traffic running on those new lanes, earthworks, drainage and road building have been under way on the northbound lanes for the past year.
The project has also involved strengthening local road networks, including extending Whangamarino Rd across the expressway. This connects communities east and west of the highway. All access is now from the Hampton Downs or Te Kauwhata interchanges.
"This section of SH1 has long had a poor safety record, so this widening and barrier work provides huge benefits for road users. We have also removed side roads and driveways from SH1, which means local people can come and go from their properties without interacting with state highway users," Coalter said.
"I want to thank local people and highway users for their patience while we get this project finished."
NZTA is also reminding motorists in rural areas including East Waikato to be extra vigilant.
"Rural roads are not designed for high speeds," Waikato system manager Rob Campbell said.
"They can be windy, narrow, have loose metal and you never know what is around the corner."
In June this year there was a fatal crash on SH25, when a motorcyclist collided with a cow.
NZ Police Waikato District Intelligence Supervisor Dr Deane Searle said farmers should check gates have been closed if they've had contractors on their farm and stressed the importance of maintaining good boundary fences.
Police receives about 500 calls about stock on East Waikato roads each year, he said.
The NZTA's safe driving tips
• Check your car is in good "health" before you head off. Check your tyre pressure and tread, windscreen wipers, indicators and lights.
• Take extra care when travelling in holiday periods because of increased traffic volumes, congestion, tiredness and people driving in unfamiliar environments.
• Drive to the conditions - whether it's the weather, the road you're on, the time of day or amount of traffic.
• Avoid fatigue. Take regular breaks to stay alert.
• Keep a safe following distance from vehicles in front so you can stop safely.
• Be patient – overtaking is unlikely to make a significant difference to your journey time because of the amount of traffic expected over the weekend.
• Allow plenty of time. Remember you are on holiday, so there's no need to rush.
• Check the NZTA's journey planner for crashes or road closures en route.
- additional reporting RNZ