UPDATED 3.25pm: The NZ Transport Agency is advising motorists that State Highway 25 is now closed following a crash this morning 10km north of Tairua.

Efforts are now underway to recover the truck and trailer unit which rolled while carrying 40 tonnes of molasses at about 8am.

A truck and trailer rolled on State Highway 25 between Tairua and Whitianga this morning. Photo: Thames Coromandel District Council/Facebook

The transport agency says the highway will remain closed for approximately one hour while the truck is being recovered.

Motorists travelling north have two alternative routes to choose from, those being SH 25A and SH25 via Thames and Coromandel.

But this will add a considerable length of time to their journey and motorists are advised to delay their journey where and if possible.

It appears the truck was the only vehicle involved in the crash, with the driver escaping with only minor injuries.

But it is being reported that an estimated 300 litres of molasses mixed with diesel had leaked from the tanker into drain.

The Waikato Regional Council are aware of the accident and the environmental risk posed, with staff currently on scene assessing the situation.

This morning's crash has caused huge delays for motorists travelling to Hahei, Hot Water beach, Whitianga and surrounding areas, with lengthy queues forming shortly after the crash.

EARLIER:

A section of State Highway 25 between Tairua and Whitianga is down to one lane after a truck and trailer unit rolled this morning.

Waikato Police say no diversion is possible and lengthy queues are forming following the crash which occurred sometime around 8am.

The crash is on the Tairua side of Whenuakite so this will affect motorists travelling to Hahei, Hot Water beach and Whitianga.

Drivers are advised that the quickest route to Auckland from the above locations is via Coromandel township and Thames.

The road is expected to be closed for several hours.

Police say the truck's driver sustained only very minor injuries. The truck had been carrying molasses at the time and fuel is currently leaking.

SunLive will update this story once more information is available.