LOS ANGELES (NBC News) - The California Highway Patrol has opened an internal investigation into a use of force incident captured on video that shows one of their officers hitting a woman in the face on a Los Angeles freeway median as she lays flat on her back.

The YouTube video titled "Police Brutality?" was shot Tuesday evening from a vehicle entering Eastbound Interstate 10 Freeway near La Brea Avenue.

It was posted July 2 and runs for 1 minute, 30 seconds and includes footage of the incident in real time and in slow-motion.

MOBILE USERS | Watch here

The man who shot the footage, David Diaz, a self-described music producer, spoke with NBC4 about what he saw.

"She took a left, and the cop, the CHP ran after her, grabbed her to try to subdue her, and then she you know, kind of tried to shove it off...Was she intoxicated? Was she mentally ill? Possibly," Diaz said.

"No one condones...when he gets on top of a woman, and this is a big officer, and he punches her repeatedly," Diaz said. "I think he punched her in the head 15 times."

The CHP said in a statement that it was "aware of the video and we are looking into the incident."

"As a matter of policy, every time there is a use of force by our officers, there is a review conducted to determine whether the use of force was appropriate," the statement said. "That will be done in this case, however, since there is an ongoing investigation, it would be premature to comment on this specific video segment without reviewing the entire incident."

They did not immediately say what prompted the initial encounter.

The video footage begins as the CHP officer is standing next to a red pick-up truck on the freeway on-ramp. He makes his way across to a concrete median where he follows a woman who is walking there and is carrying a white bag.

Moments later, the officer tries to grab the woman's arm as she appears to resist.

As he tries to gain control over the woman, he throws her to the ground. While the woman is on her back, the officer holds her down delivers about a dozen hits to her head and upper body in about 11 seconds.

"These are like, grown men, on top of you punching you to a point where she could've died out there," Diaz said.

As the officer his hitting the woman, who was not immediately identified, she appears to be use her arms and hands to protect her face. A second man joins the officer to help control the woman as she is placed in handcuffs.

Another witness who did not want to be identified told NBC4 the woman "did not look well, mentally," when she was walking along the freeway.

The woman was "carrying a lot of bags" and was not wearing shoes, only black socks, the witness said.

After she was brought down to the asphalt by the officer, the woman put her arms up "trying to guard herself," the witness said. "She looked terrified...she just looked gone."