One person has serious injuries after a crash on State Highway 1 near the Atiamuri dam.

A police spokeswoman said the person had been trapped following the crash between a truck and a small van between Thorpe and Walnut Rds.

They have been freed and taken to Waikato Hospital.

State Highway 1 has re-opened to one lane but diversions are also in place down Oruanui and Tirohanga Rds.