A teenage asylum seeker who was left with a fractured skull and a blood clot on his brain in a "savage" attack may have been set upon by a gang who had been drinking in a nearby pub, police said.
The 17-year-old, a Kurdish Iranian, is fighting for his life in hospital after being targeted by around eight people in what detectives are treating as a hate crime.
After discovering he was an asylum seeker, they chased after him and launched their attack, repeatedly kicking him on the floor and aiming blows to his head.
Chief Superintendent Jeff Boothe, Croydon's borough commander, called it a "savage attack" and said it was only the intervention of passers-by and the arrival of police that stopped it being worse.
The attack has prompted a wave of condemnation, with Tory minister Gavin Barwell, Croydon Central's MP, describing the attackers as "scum".
Mr Boothe said: "A number of bystanders and eyewitnesses tried to intervene and say to the attackers that enough is enough.
"By all accounts they didn't actually stop until the sound of police sirens were heard in the background."
The incident happened in Shrublands Avenue at 11.40pm on Friday.
The boy is in a critical condition while his two friends escaped with minor injuries, Scotland Yard said.
Officers believe some of those involved had been drinking in The Goat in Broom Road, Mr Boothe added.
The "close-knit community" has been left shocked by the ferocity of the attack, he added, and extra officers have been out and about to reassure people.
He said: "This is not usual for the area, it is out of the norm. This is not Croydon, Croydon is a very diverse community - they celebrate their diversity and as recently as Thursday at the town hall we had a number of leaders from different faith groups saying we are all united and stand together."
He added: "Hate crime is something which we understand can be very, very divisive. Croydon is culturally diverse and we need to continue to celebrate that.
"We are appealing to all decent people from whatever background they come from to help us identify the individuals that are involved in this isolated attack."
And, in a direct message to the attackers, Mr Boothe said: "Hand yourselves in. It's only going to be a matter of time before we identify and locate them. We would ask them to do the decent thing and hand themselves in."
Anyone with information should call police on 101 or Crimestoppers on 0800 555 111.