Whanganui East resident Cara Davis told the Chronicle she was going home from Whanganui Hospital about 3am on April 20, and discovered the man on the road.
"I came round the corner into Tinirau St and saw a guy lying on the road unconscious," Davis said.
"I rang the police and ambulance but I was by myself so I didn't want to get out of the car.
"The police turned up pretty much straight away. They couldn't wake him and took him away in the ambulance.
"It was pretty heart-wrenching ... I'm still shaken up about it. I hope they can find out something about it."
Davis said the man was lying at the Duncan Street roundabout end of Tinirau St.
Police want to hear from anyone who saw or heard anything out of the ordinary in the area in the early hours of the morning on April 20.