A milk tanker has skidded off State highway 56 near Opiki, south of Palmerston North, ending up on its side and spilling part of its load.

Minutes after filling up the tanker with 27,000 litres of milk at Fonterra's Longburn plant the driver lost control of the vehicle which then crashed through a fence and came to a stop in a paddock with its trailer tipped over.

No other vehicles were involved and the driver was unhurt.

The man had left Hawera this morning and was heading to Wellington to catch the ferry to Picton.

Tokomaru volunteer fire brigade attended the scene along with ambulance and police.

Chief fire officer Mike Davis said because the soil had been recently ploughed it was acting as a sponge for the milk and fire officers had contained the spill in a storm water drain.

''It's classed as a hazardous substance so it needs to be contained.''

Horizons Regional council pollution experts were expected to attend.

The highway remains open but is down to one lane with stop/go signs in place.

It is unknown yet what caused the truck to leave the road on the state highway which is lined with potato and maize paddocks.

The accident comes two months after a petrol tanker crashed in Shannon spilling thousands of litres of fuel across the town’s main street.

- © Fairfax NZ News