Police are speaking to a 19 year old driver who they say left the road, hit a street sign and then struck a visually impaired pedestrian who was walking on the footpath in Morrinsville.

The visually impaired man, who's in his 20s, has been airlifted to Waikato Hospital in what's believed to be a serious or critical condition.

The crash happened on State Highway 26 leading to Hamilton, where the speed limit changes from 50 kilometres an hour to 70.

Serious crash investigators are at the scene.