The police serious crash unit will be investigating.
The road closure will allow emergency workers to clear the scene, and traffic delays can be expected. Drivers are asked to be patient and to follow directions.
A three-vehicle crash blocking SH29 over the Kaimai Range ws also delaying motorists, but the road had just re-opened in both directions.
Two cars and a van collided about about midday.
Police are urging motorists to use SH2 through the Karangahake Gorge or to go via Mamaku while contractors clear the road.
One woman suffered pelvic injuries, and two others were injured in the crash.
Meanwhile, in Taranaki, a crash near Inglewood, south of New Plymouth at 12.30pm delayed drivers but the road was now open to all traffic.
One person suffered minor injuries in the two-car crash at the SH3 intersection with Dudley Rd.
In the big cities, the Christmas Eve rush to escape to holiday hotspots is on.
It is raining in Auckland and transport authorities are warning of "heavy congestion" southbound on the Southern Motorway.
The New Zealand Transport Agency is asking motorists to consider delaying their departures to avoid congestion.
An agency spokeswoman said the usually 45-minite trip between Highbrook and Papakura was now taking an hour.
"It's a little bit heavier than normal. It's heavy but it's flowing. Things are still moving," she said.
She asked motorists to "take it easy", be patient and respect others.
"Everyone's in the same boat."
There have been a number of minor crashed around the city today.
On the Northern Motorway, traffic is building around Wellsford, where there is congestion.
The drive through to Warkworth was looking good after that, the spokeswoman said.
North of Wellington, congestion on the Kapiti Coast between Paraparaumu and Waikanae had eased. Down south, traffic was light in Christchurch and Dunedin.
Full list of hotspots go to tinyurl.com/z9apfk4
