Footage of the incident, which unfolded on the Pacific Highway at Lake Munmorah, was recorded by another driver's dashboard camera and shared widely on social media.

The video shows a man in a yellow T-shirt approach a woman standing on the passenger side of a ute before punching her in the head. The woman reels back before getting into the passenger seat of the car.

The footage was posted online by Dwayne Pillidge, who wrote that the incident occurred on Monday after the woman threw objects at the man's car.

"This is after the woman in the front car was tossing things from her window at his car," he wrote. "I don't care what your reason, it is not ok to hit a woman."

The video has been shared more than 1,400 times and attracted 3,500 comments since being posted.

Many commentators were scathing about the man's behaviour, describing it as cowardly and gutless, while others pointed out that the video may not give the full story behind the attack.

Tuggerah Lakes Local Area Command duty officer, Chief Inspector Col Lott, said the violence shown in the video was unacceptable.

"Obviously with any video footage we're only getting a snapshot of the whole incident," he said.

"It depicts a male walking up to a female and punching her in the face. Assault of any sort is unacceptable, especially assault to a female.

"If you have a problem with somebody in a road rage situation, somebody has done something wrong, the appropriate channel is to inform the police and let us deal with the matter, not to take it into your own hands.

"Assault of any kind is not acceptable, especially assault of a female. It won't be tolerated."

The driver who captured the altercation, Dwayne Pillidge, told 9NEWS the man was throwing what appeared to be pieces of wood at the woman, who had stopped at a set of traffic lights.

"She was sitting on the window sill and it looked a little bit like maybe small pieces of wood, they were white, but it definitely wasn't rocks or anything like that," he said. "They travelled more like a piece of wood being thrown."

Police are urging any witnesses to the incident on the Pacific Highway at the intersection of Elizabeth Bay Drive at Lake Munmorah to come forward or contact CrimeStoppers.

The woman involved in the incident has contacted police and is expected to make a formal statement on Tuesday afternoon.