"Merge with extra care in passing and expect delays through this area."
A witness told the Herald she was driving in the opposite direction when she saw a vehicle suddenly fly into the air.
"It was full flying in the air," she said.
"I just saw it flip about three or four times in the air before landing."
The woman said she could not see what may have caused the car to flip in the first place and did not see the aftermath, as she could not stop.
"It was quite freaky ... there's going to be a big traffic jam."
A St John spokeswoman said an ambulance was called to the scene at 11.39am after reports of a motorvehicle accident.
One person had been treated in a moderate condition and is being taken to Auckland City Hospital.