Police will shortly re-open part of State Highway One in the central North Island which was closed after an oil spillage caused cars to slip off the road and a truck to jack-knife.
An estimated 2300 litres of transmission fluid leaked from a truck for 117km southbound between Waiouru and Sanson, from 2.30am onwards.
Police say rain combined with the fluid to make the road extremely slippery.
Grit is being laid on the road in the worst affected places.
Three or four cars had minor crashes and a truck jack-knifed on the road at Ohingaiti, south of Taihape, blocking the road completely.
Police say northbound traffic is believed to be OK.
A diversion is being put in place at Ohingaiti.
Inspector Marty Parker told Morning Report that luckily, the driver of the truck that caused the slick, identified the problem at Sanson - otherwise he could have made it all the way to Wellington and the spillage would been much worse.