Police have released "shocking" footage of a brutal unprovoked assault on a man as he lay defenceless in a pool of blood on a tram platform.
The 49-year-old victim was repeatedly kicked and stamped on the head after he was knocked unconscious at the Metrolink station in Chadderton, Greater Manchester.
Detectives are treating the attack as attempted murder and said it was "pretty incredible" how the victim survived his ordeal and is now on the road to recovery.
The assailants are all described as Asian males aged between 15 and 18.
The victim was targeted as he stepped off the tram at the Freehold stop at about 9.35pm on Thursday March 8.
His attackers returned on three separate occasions to continue the remorseless assault and only made their escape when the driver of a tram travelling in the opposite direction, supported by passengers, forced open the doors and ran to his aid.
Detective Sergeant John Coleman from Greater Manchester Police said: "Not only did these men target an innocent man for no apparent reason, they subjected him to a sustained and brutal attack and the footage is absolutely shocking.
"How anyone could kick a defenceless man in the head as he lay unconscious is almost unbelievable but for them to return on three separate occasions to continue their assault and then leave him bleeding on the platform is beyond comprehension.
"The fact the victim not only survived but is now on the road to recovery is pretty incredible.
"We know a tram stopped on the opposite side of the tracks at the time of the attack and I would urge anyone who has any video footage to please send it in to us as a matter of urgency. It could be vital to finding the people responsible.
"Alternatively, anyone who thinks they know who did this, or has any information, please get in touch. This could have been your father, son or brother and we need to find these men immediately."
Transport for Greater Manchester's head of Metrolink, Danny Vaughan, said: "This was a sickening and sustained attack that has left a man seriously injured.
"We know there's been a spike in the number of incidents of crime and antisocial behaviour in the Oldham area recently. It is something we are working with partners to try and tackle but the extent of this assault and level of force used was indiscriminate and wanton."
Anyone with information should contact police on 0161 856 8267 quoting reference number 2239 of 08/03/18 or call the independent charity Crimestoppers anonymously on 0800 555 111.