Police are investigating a sickening road rage attack at a busy intersection on the NSW Central Coast early on Monday afternoon.

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.