A crash at on State Highway 29 between a light truck and the car closed the road at the Kaimai Range this afternoon.
One person has life-threatening head injuries and another has serious injuries following a car and truck collision shortly before 2.14pm today.
The other two occupants of the car have moderate injuries and the condition of the truck driver is not known.
The road was closed, but has since reopened.
The Automobile Association's general manager of motoring affairs, Mike Noon, said with sunny, clear conditions forecast for most of the country people needed to take extra care in the mornings and evenings.
"The low winter sun can make sun-strike a real problem at either end of the day and the clear conditions mean there will likely be some frosts and icy roads in places."
From May through to August is the worst time of the year for sun-strike crashes which normally involve a driver pulling out in front of a vehicle they didn't see or rear-ending a vehicle stopped in front of them.
Mr Noon said the fine weather was also likely to mean a lot of traffic on the roads this long weekend, so drivers should expect some delays and try to avoid travelling at the peak times of Friday afternoon, Saturday morning and Monday afternoon if possible.
Superintendent Steve Greally said while police wanted New Zealanders to enjoy themselves this long weekend - the last public holiday until October - they also wanted to make sure safety was put first.
An interactive map of the potential holiday congestion is available on the agency's website.
"It only takes a split second to lose control of a vehicle in wet or icy conditions."
It was crucial motorists drive to the conditions, Mr Greally said, and this weekend police will be focusing their attention on high-risk behaviour using a combination of preventive and enforcement measures.
Over Queen's Birthday weekend last year, five people were killed in five separate road incidents - three were drivers and two were passengers, one of whom was on a motorcycle.
There were also 96 crashes which caused injury, including 28 people who were seriously hurt and 109 who suffered minor injures.
And for the first time, the New Zealand Transport Agency has crunched the numbers from previous holiday periods to work out where and when traffic is likely to be the heaviest.
In Auckland and the Bay of Plenty, the pinch points today will be State Highway 1 southbound near Takanini between 2pm and 7pm, and on Monday, southbound on SH1 between Puhoi and Wellsford from 11.30am to 5.30pm and westbound on SH2 between Paeroa and Tauranga from 11am and 2pm.
