Auckland man Chris Gregory was heading back home along SH1 when he came across the accident.
"I was in a line of traffic about 250m from the incident. I got out of the car and walked down. It appears that the driver in that car was walking and standing, albeit looking a bit dishevelled, with a bit of a blood stain."
Gregory said the driver of the Mazda told him he was allegedly hit by an oncoming vehicle and tried to get out of the way but had no luck.
"He tried to avoid it and the result is what you see [in photo]."
He says traffic still isn't moving and he doesn't expect it to in the near future so he's taken a short cut through Karapiro to get back to Cambridge.
"They obviously hit at quite a pace."
It was the second accident he'd witnessed in the past few days after witnessing one on the northwestern motorway by Western Springs.
"So I'm taking it very easy today."