A crash involving two trucks has completely blocked the northbound lanes of State Highway 1 south of Auckland.
Police said they were called to the crash at Pokeno just before 1pm.
One person has been seriously injured and a helicopter has been dispatched.
The Transport Agency said one northbound lane was open but detours were in place for State Highway 2 traffic, and drivers could expect delays.
SH1 POKENO OFF-RAMP, SOUTHBOUND - CLOSED - 2.45PM— NZTA Akld & Nthlnd (@NZTAAkl) February 14, 2019
The #SH1 southbound Pokeno off-ramp has been CLOSED due to a serious crash. Please detour via Mercer and allow extra time for the detour route. Updates here: https://t.co/LCdaISEcz7. ^MF pic.twitter.com/1Iik3Ic3aA
Another crash has closed the southbound off-ramp to Pokeno.
The Transport Agency says this will impact on the detour for motorists travelling from SH2 heading for SH1 to Auckland.
Motorists are being advised to delay their travel until alternative detours are set up.
A third crash is now partially blocking lanes just north of Mercer near Pioneer Road.
SH1 PIONEER ROAD MERCER, NORTHBOUND - CRASH - 3.55PM— NZTA Akld & Nthlnd (@NZTAAkl) February 14, 2019
A NEW crash is partially blocking lanes just north of Mercer near Pioneer Road. Please note there are 2 other crashes in the area. Consider delaying your journey or be prepared to use alt route. https://t.co/HcL8dsqWgi. ^MF pic.twitter.com/AG9Xvxlhzo