A Fire and Emergency New Zealand spokesperson said four crews from Waipū, Kaiwaka and Maungaturoto attended.
Two people were trapped and rescued, the spokesperson said.
A crew from a Whangārei-based Northern Rescue Helicopter assisted the Auckland Westpac Rescue Helicopter and landed on top of the Brynderwyns to help emergency services.
The Serious Crash Unit has been notified, a police spokesperson said.
“The road will be closed for several hours and traffic management remains in place.”
Southbound traffic is diverted through Waipū and northbound traffic is diverted down SH12 towards Dargaville.