One person's died after being involved in a car crash and then being hit by a vehicle travelling in the other direction on the Waikato Expressway this afternoon

A car was travelling north on State Highway One near Auckland's Hampton Downs when it's believed to have rear ended a truck.

An eyewitness says the man was in a car that was screaming past everybody before crashing, then he got out of the car and ran into the southbound lane where he was hit.

Lanes in both directions remain closed while a scene examination's underway.

Detours are in place.