A 15km diesel slick stretching from the top of the Rimutaka Summit to Featherston has turned a major Wellington highway into an iceskating rink.
Police are warning motorists to take extra care after fuel was spilled across both sides of the road.
There is so much diesel across the road it threatens to cause vehicles to slide and crash.
A spokeswoman said it stretched about 15km from the top of Rimutaka Hill to the Wairarapa township of Featherston.