(CNN) -- Brenda Cruz and her family were flabbergasted by what they spotted as they were driving on Interstate 77 in North Carolina this weekend: A man was hanging on to the back of a fast-moving white sedan in the right-hand lane.
"All of a sudden the kids say, 'There's someone on top of the car on the trunk,' and I'm like, 'What?'" Brenda Cruz told CNN affiliate WSOC.
The man was lying across the outside of the car's trunk, she said, as the vehicle sped along at around 50 mph Saturday afternoon.
She pulled out her cellphone and began to film the bizarre scene as other cars on the road slowed down, waiting to see what would happen.
The family said they witnessed the man shattering the rear windshield before clambering inside the moving vehicle, which was being driven by a woman and had a child in a car seat inside.
"Whenever he lifted his hand to smash the glass open, it looked like it was something sharp," Brenda's 17-year-old son, Samuel, told WSOC, saying he was concerned about what might have happened next.
"I'm really worried because I just hope she's OK, you know, with her kid," he said.
Authorities haven't figured out yet what exactly was going on. By the time they responded to calls, the white sedan had gone.
Neither the man nor the car have been located, but officers are still looking into it, Patty McQuillan of the North Carolina Department of Public Safety told CNN on Sunday.
Authorities told WSOC that they think the driver and person on the back of the car know each other, but they can't be sure until they establish who they are.