Police are investigating after dashcam footage emerged of a shirtless man getting out of his car and running to punch another driver through an open car window, before going back for a chainsaw, during peak-hour traffic in south-west Sydney.

Vision from Dash Cam Owners Australia's Facebook page showed a white Jeep blocking traffic while trying to cross three lanes and double lines to turn onto Horsley Drive in Fairfield on Tuesday.

A topless man is seen getting out of his vehicle from three cars behind and sprinting down the road to confront the Jeep driver.

He then punches the man through the window before the two begin brawling amid the busy traffic.

Another man in high-vis then joins the fight, which eventually ends in the shirtless man being pinned to the road by the other two men.

After exchanging a few words, the attacker walks back to his car, where he pulls out a chainsaw; however, the Jeep has already driven away.

The video has been viewed more than 170,000 times, with more than 2,000 comments.

"Patience and road courtesy, where has it gone? Couple of trucks being courteous and one idiot thinks he owns the road and has the right to start belting people, maybe he will learn from this," one person wrote.

"That's super scary! Could have been a young mum with kids in the car when aggressive guy came out of nowhere fists punching! I hope old mate was reported to the police!" another said.