A BMW driver pulled out a sword and slashed a fellow motorist's arm when a heated exchange erupted into sickening violence on the road.
The lorry driver was left with what police termed "a serious arm injury" after his road rage attacker - who had been behind the wheel of a silver BMW 1 series - suddenly produced the weapon and plunged it into his victim.
Police said the ugly scenes played out after "a disagreement" on Crosby Road South at the junction of Knowsley Road in Bootle on Thursday.
Today police urged any witnesses or anyone with dashcam to come forward after the attack which happened around 5.30pm.
A police spokesman said: "At 5:30pm officers were called to Crosby Road South at the junction of Knowsley Road following reports that two men, the driver of a HGV lorry and the driver of a silver BMW 1 series, had become involved in a disagreement.
"The driver of the lorry, a 25-year-old man was assaulted with what was described as a sword. He has been taken to hospital for treatment to a serious arm injury."
A van driver thought to have stopped at the scene was also urged to contact police.
Police are also carrying out CCTV enquiries.
Detective Inspector Catherine Walsh said: “We are in the very early stages of an investigation and I would ask anyone who witnessed the incident, or has any information, to please get in touch. We are particularly interested in talking to a potential witness who we believe stopped at the scene in a blue van.
“A young man has been left with serious injuries following this incident. If you saw a vehicle fitting either description in the area, or have CCTV or dashcam footage, please let us know. Any information could prove vital to the investigation.”
A 41-year-old man has been arrested on suspicion of assault and has been taken to a police station to be interviewed.
Anyone with information is asked to contact @MerPolCC, 101 quoting ref 19100742124 or @CrimestoppersUK, anonymously on 0800 555 111.
You can now tune in to the Liverpool Echo's early-morning news headlines on the Amazon Echo and other Alexa-enabled devices.
Click on this link and then open up the Echo's briefing service in the Amazon Alexa app.