A busy Waikato road's been blocked off by a crashed truck.

The empty tanker has hit a power pole on State Highway 27, just south of the Mangawara Road intersection.

Police say the truck has been moved out of the way, but power lines are strewn across the road.

It's expected to be closed for around an hour.

Drivers can use State Highway 1 to the west, or State Highways 2 and 26 to the east as alternate routes.