Diversions are in place and the road is closed between Henley Rd and Carol Leon Ave.
The detour is via Peak Rd.
The second crash was at the intersection of Matakana Rd and Riverglade Lane in Matakana. A car and motorbike collided around 3.40pm.
One person was seriously hurt and one had minor injuries, according to St John. One ambulance and a helicopter attended the incident, with both patients taken to Auckland Hospital.
Matakana Rd is closed and the NZTA urged motorists to expect delays or delay travelling.
The Serious Crash Unit has been advised of both crashes.
The crash is causing chaos for people trying to get to the Bryan Adams concert, two minutes up the road at Matakana Country Park. Dave Dobbyn was to open the gig, which started at 4pm and ends at 10pm.
A Matakana Liquor Centre staff member said it appeared emergency services were letting cars through the crash site very slowly.
"We can only see so far each way but it's backed up as far as the eye can see," he said.
A Gull Station employee said traffic heading toward Warkworth along Matakana Rd had come to a complete standstill.
"It's moving coming out of Warkworth but it's fairly heavy."
As of 4.45pm she understood the accident had been cleared from the road, but fire engines and police were still in the area. A helicopter had also left the scene but sounded like it was returning, she said.
