US man hangs onto speeding car

Incredible vision has surfaced of a man clinging to the back of a car travelling at more than 80km/h on a busy US highway.

Motorists on North Carolina's I-77 were taken aback as the man held onto the boot of the car, which witnesses say was driven by a woman and had a young child inside.

Brenda Cruz was travelling behind the vehicle with her family and was able to film the dramatic incident on her phone.

Ms Cruz's son Samuel said the man was able to break the back windscreen and climb inside.

"Whenever he lifted his hand to smash the glass open it looked like it was something sharp," he said.

"I'm really worried because I just hope she's OK you know, with her kid."

Authorities searched the area after receiving numerous calls about the incident but were unable to track the car down.

They suspect that the man and the female driver are known to each other but have few other leads.

Should charges be laid, they said, the driver would ultimately be held responsible.