Traffic heading north is being diverted via Paterson Rod.
Motorists travelling south would be diverted at Station Rd via Kaitangata.
Police said drivers should follow the directions of traffic management staff at the scene and northbound trucks were requested to take an alternative route because the diversion wasn't safe for heavy vehicles.
Meanwhile, a person has been left with serious injuries after the light truck they were in crashed into a rock face on the Otira Highway between Otira and Arthurs Pass about 10am.
The road is blocked and is expected to stay closed for about two hours.
One person was seriously hurt, a police spokeswoman said.
The injured person was trapped in the vehicle, but has since be freed and taken to Christchurch Hospital by helicopter.
No one else was injured.
The incident happened on a stretch of highway between Settlement and West Coast roads, a police spokeswoman said.
The truck had been carrying scaffolding, it clipped another vehicle from behind for hitting the rock face, police said in a statement.
In Northland, emergency services were also responding to another crash.
They were called to the scene on Waimate North Rd at 11.08am.
That incident is believed to have happened 1km from a one-lane bridge, between Okokako and Montrose roads, a police spokeswoman said.
No one was believed to have serious injuries and a tow truck had been called, a police spokeswoman said.
Earlier this morning, two people were trapped after a van and another vehicle crashed in rural South Auckland.
They've since been freed.
A St John ambulance spokeswoman said two people had moderate injuries after the 7.45am incident, which happened on Tuakau Bridge-Port Waikato Rd, about 300m west of Te Awamarahi Marae.
Another minor crash at Huntly is expected to cause delays for rugby fans travelling to Hamilton for tonight's Kiwis-Tonga Rugby League World Cup match at Waikato stadium.
A truck hit a barrier on the motorway near Ohinewai, just after 8am.
The driver wasn't injured.
The truck was blocking the southbound lane on State Highway 1 and southbound traffic was being diverted onto Ohinewai South Rd, at the Tahuna Rd intersection.
Drivers travelling north were also being diverted on to Ohinewai South Rd, near Fisher Rd.