Several people have been arrested after a teenage asylum seeker was beaten up and left unconscious.
Someone who saw the attack in southeast London said the victim was "absolutely beaten up - kicked, mostly in the facial area".
Six men and a woman, aged between 20 and 26, and a 17-year-old girl, have been arrested and taken into police custody in connection with the incident.
A 20-year-old woman, arrested on Saturday, has been released.
Detectives are continuing to appeal for information and witnesses to the attack, which is being treated as a suspected hate crime.
The 17-year-old asylum seeker, a Kurdish Iranian, was waiting at a bus stop with two friends at about 11.40pm on Friday when they were approached by a group of eight people.
After discovering he was an asylum seeker, they chased him and launched a "savage" attack including "repeated blows to the head", police said.
Someone who lives in Shrublands Avenue, where the attack happened, said: "There were more than eight people. There was a massive group coming up from The Goat pub.
"You couldn't see who was hitting who.
"There was one person, the one who ended up in hospital, he was getting absolutely beaten up - kicked, mostly in the facial area. He was getting kicked and punched by everyone."
The resident added: "There was a group of roughly 10 people that was kicking and punching him, and the rest, another 10 or 20, were all just around watching.
"Then when they heard sirens they started to go. People that were there, witnesses, because they couldn't do anything against a group of 30 people, they had to wait until they moved off and that's when they managed to help him.
"That's eventually when the ambulance and police (arrived), and that was it."
The teenager remains in hospital in a serious but stable condition with a fractured skull, a blood clot on his brain and facial injuries.
His two friends escaped with minor injuries.
DS Kris Blamires, from Croydon CID, said: "A number of people came to the aid of the victim as he lay unconscious and injured following the assault.
"The suspects are believed to have made off in the direction of the Goat Pub, Broom Road following the attack.
"I would encourage all those who came to his aid and those in the immediate area who witnessed the attack or saw the males leave the scene to get in touch.
"All communities stand together against hate and we would ask anyone with any information to come forward immediately."
The local community has been left shocked by the ferocity of the attack, and extra officers have been out and about to try to reassure people.
Croydon Central MP and Conservative minister Gavin Barwell described the attackers as "scum".
"I think most people in Croydon will be as appalled as I am that what appears to have happened is a young man who came to this country seeking sanctuary has apparently been targeted because of his ethnic background," he said.
"It's an appalling crime and I hope the people responsible are caught quickly and receive the full force of British justice."
He said Croydon generally had "very good relations between people of different backgrounds".
"This is completely out of character but that is no comfort to the individual who is fighting for his life now," he added.
:: Anyone with information should call police on 101 or Crimestoppers on 0800 555111.