A Manitoba man says he came across the horrifying aftermath of a weekend hit and run that sent an 18-year-old man to hospital in critical condition.

Wayne Towns was driving south on Lagimodiere Boulevard at the South Perimeter Highway overpass at about 3:45 a.m. Sunday when a young woman stepped in front of his vehicle and waved him down.

She told him she had been walking on the other side of the highway with her boyfriend and they had been arguing when he stepped into the middle of the highway and was struck.

"She was just really freaking out. She just was screaming, 'he got hit, he got hit,'" Towns told CBC News.

"She was yelling and screaming, her arms were waving up and down, just running back and forth. She was in shock, I guess," he added.

"She just kept on screaming, 'I don't know what to do. I told him to get off the highway and he wouldn't listen to me. I told him to get off the highway a few times and he wouldn't listen to me,' she kept on saying."

The 18-year-old man remains in hospital in critical condition, police said on Monday.

A 27-year-old man has turned himself in to police and is facing charges of failing to remain at the scene of an accident and driving without a licence.