The NZ Transport Agency said there had been a serious crash just before the summit on SH29 in the Kaimai Range. Drivers heading to the Bay of Plenty should expect delays and avoid the area if possible.
Traffic is building on SH26, south of Paeroa. This is a common hotspot for holiday traffic.
Auckland's motorway network was running smoothly today but a truck breakdown southbound on the Southern Motorway near the Grafton Rd overbridge this afternoon was now causing delays.
"Today we traditionally expect a lot of people to starting leaving the main centres and making their holiday getaway," a transport agency spokeswoman said.
"People should allow plenty of time for their journey so they don't get impatient. When they get impatient, that's when they make bad decisions. Plan well and allow plenty of time for your journey."
In Hamilton, bargain hunters heading to Te Awa/The Base mall in Te Rapa are advised to expect delays. Police Senior Sergeant Andrew Townsend said traffic was "crawling" along Wairere Drive and Te Rapa Rd.
"There have been three non-injury motor vehicle crashes on Wairere Drive since 9am, including a seven-car non-injury crash. Police request all drivers to not be distracted and be patient if you are travelling to the Boxing Day sales," he said.
The first signs of holiday traffic build-ups are emerging on the Waikato Expressway. The transport agency has advised drivers to "expect significant delays southbound on the Waikato Expressway at Pokeno for traffic turning left on to SH2" heading towards Coromandel and Bay Of Plenty.
In Wellington, traffic is building on State Highway One at the Mana Esplanade, a 50 km/h pressure point north of the city. Northbound traffic is also heavy from Raumati to Waikanae, but is moderate through Otaki.
Most of the crashes on New Zealand's roads have been "very low level" and could have been avoided if motorists stuck to simple rules, the country's top road cop said.
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"It's Russian roulette when people take stupid risks and get into situations they cannot handle," Superintendent Steve Greally told the Herald.
"It's a hard way to learn a lesson that people should know from the beginning."
Causes of crashes so far included speeding, using mobile phones while driving, inattention and driver impatience.
He said the fatal crash last night was "horrific".
"We have now got a family living their first day without their loved one. It's the families that lose out the most."