Police said that a group of about 20 people were involved in the attack on the 17-year-old in Croydon, south-east London, which they said was being treated as a hate crime.
The Press Association said the teenager was Kurdish Iranian and suffered a fractured skull and a blood clot on his brain. Police have not identified the victim.
Four people were charged with violent disorder, and one with violent disorder and grievous bodily harm, police said, They will appear in court later.
Teenager in hospital
The teenager was still in hospital Monday, where his condition was described as "serious" but not life-threatening.
The Metropolitan Police said they were called to the scene at 11.40pm Friday. Detectives believe that a group of suspects approached the victim as he waited with two friends at a bus stop outside The Goat pub.
Detective Inspector Gary Castle, from Croydon criminal investigation department, said in a statement Monday: "We now know that a large number of people, approximately 20, were involved in the attack on the victim."
He added: "It is understood that the suspects asked the victim where he was from and when they established that he was an asylum seeker they chased him and launched a brutal attack.
"He sustained serious head and facial injuries as a result of this attack, which included repeated blows to the head by a large group of attackers."
One resident told the Press Association: "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."
Detective Inspector Castle said a number of people helped the victim as he lay unconscious. His two friends escaped with minor injuries.
Police arrested six men and three women -- ranging in age from 17 to 26 -- over the weekend.
Mayor of London Sadiq Khan posted a statement on Twitter saying: "Hate crime has no place in London, Britain or anywhere else."
Jeremy Corbyn, leader of the opposition Labour party, also condemned it. "Absolutely shocked at attack on young Kurdish asylum seeker, who came here searching for safety. I fervently hope he makes a full recovery."
Director of Advocacy at the Refugee Council, Dr Lisa Doyle, said: "We're disgusted to hear that a young man who fled to this country in fear of his life has been subjected to such a vicious hate crime in the very place he hoped to find safety. "
According to the Refugee Council, 30,603 people applied for asylum in the UK last year. Of these, 2,666 were from Iraq, which was the third biggest source of asylum-seekers behind Iran and Pakistan.