"I have never seen so much blood from one person. I feared he wouldn't have made it through."
The victim was transported to Auckland City Hospital and remained there this afternoon.
One member of the public attempted to fight off the group of attackers but was outnumbered, the witness said.
The attackers were seen fleeing the incident on foot. No one has been arrested.
A police spokesperson said the victim was knocked to the ground and suffered serious injuries.
Another man, who had been involved in the "disorder", sustained minor injuries.
The spokesperson said inquiries are continuing.