A 50km/h temporary speed restriction is in place, and people are asked to travel with care through the area, New Zealand Transport Agency Waka Kotahi said.
Special fire appliances from Dunedin were dispatched to the scene where a truck and trailer carrying an excavator rolled and was leaking diesel.
A Fenz spokeswoman said the crash happened about 6.40pm yesterday, between Lawrence and Waitahuna.
Crews from Lawrence, Waitahuna and Milton responded initially, and "a support vehicle" was sent from Dunedin with "some extra absorbent material" to help clean up the spills.
The spills were believed to be a mixture of fuel and hydraulic oil, and the Dunedin unit was sent to ensure it did not leak into nearby waterways.
A police spokeswoman said the excavator was down a bank, and the truck and trailer were partially blocking SH8, and the road is now closed between Clarks Flat Rd and Waitahuna West Rd.
There were no reports of injuries, she said.
- Allied Media
