A spill of about three cubic metres of expanding concrete on Dunedin's Southern Motorway caused major traffic delays this morning.

Police say a northbound concrete truck had to slam on its brakes travelling uphill just south of Lookout Point.

Its load spilled on to the road about 9am, causing what police say was ''a hell of a mess''.

The wet concrete was shifted from the road to a nearby paddock, and the road cleared by late morning.