The motorcyclist was initially in a serious condition but St John crew at the scene upgraded the man, aged in his 50s, to critical.
Fire and emergency crews had prepared a landing pad for the Auckland Westpac Rescue Helicopter to transport the man, who suffered multiple injuries, to Auckland City Hospital.
Fire and Emergency NZ shift manager Daniel Nicholson said northbound traffic was being diverted up the Tapu-Coroglen Rd, but it was unclear whether southbound traffic was being turned around or given an alternative route.
Cherry said they were aware closing the road would cause frustration for motorists but he urged people to be patient.
"I know there's been a lot of traffic offences from Auckland members of the public travelling home. I'd like to ask people just to take their time and be patient."
Fire crews have been at cordons at Manaia Rd and Kereta Bay, helping divert traffic.
Nine people died on New Zealand roads during the Christmas and New Year period - the lowest number of fatalities for the festive season since 2013.
But police are still asking motorists to take care during the summer holidays.
The crash comes after a pedestrian was critically injured after being hit by a truck in Whangārei last night.
The person was taken to Northland Hospital by ambulance.
A woman was also seriously injured when her car crashed into a ditch on Old North Rd, Timaru, about 10.30pm yesterday.
She was airlifted to hospital for treatment.
The official holiday road toll period spanned 9.6 days this year - running from 4pm on December 24 until 6am yesterday.
A total of 380 died on the roads last year, the worst annual road toll in nearly a decade.
