A crash involving two trucks near Huntly today was caused by a driver falling asleep behind the wheel, police say.

The trucks collided on State Highway 1 about 8.30 this morning, spilling diesel over the road.

The drivers escaped injury.

The highway was closed until just after midday, causing considerable delays to motorists, Waikato road policing manager Inspector Freda Grace said.

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"On this occasion it appears the driver of a truck-and-trailer unit fell asleep at the wheel, colliding with another truck," she said.

"Driving conditions do not solely relate to weather; they also include the driver and vehicle fitness for the road.

"Fatigue in drivers can have significant consequences. Tired drivers can kill, tired drivers can cause serious harm."

Another fatigue-related crash occurred on State Highway 1 between Rangiriri and Ohinewai just hours earlier, Mrs Grace said.

A car hit a barrier at 6.15am.

The driver, who was alone, was uninjured.

"Our message is ensure you are a well rested, and drive to survive," Mrs Grace said.