Daniel Laskos, 16, was knifed during a fight involving a number of youths on Church Road, Harold Wood shortly after 6.40pm on Friday.
Witnesses said machete-wielding thugs wearing balaclavas ambushed Daniel as he came out of his local convenience shop.
Ten minutes later, two boys aged 15 and 17, were found with stab wounds in nearby Retford Road.
The pair were arrested on suspicion of murder in hospital but have since been discharged into police custody.
Three more males, 18, 20 and 24, have been held over Daniel’s murder.
His uncle John said Daniel’s family had come to London from the Czech Republic about a decade ago.
He added: “He was a lovely boy. His mother is devastated. We have no idea why this happened.”
Daniel attended Lammas School and Sixth Form in Leyton. He successfully completed Year 11 and left to become a plumber, the school said.
A spokesman added: “Our thoughts and prayers are with Daniel’s family and friends at this difficult time.
“Daniel was well liked by staff and pupils. He successfully completed year 11 before leaving the school and was training for a career as a plumber.”
A shop worker said: “The boy who died was in the shop with a friend.
“When they left, about four or five young boys ambushed them. There were lots of knives. It was terrifying. One boy had a neck wound. Horrifying.”
He added: “The boy who died used to come on the shop regularly. There was never any problem with him. It’s a tragedy for his family.”
Daniel’s killing - the fifth homicide in six days in the capital - happened close to the park where girl scout Jodie Chesney, 17, was murdered in March 2019.
He is the 13th teenager to die in a knife attack this year, just two short of the 15 killed in 2020 and on course to overtake the figure of 26 in 2019.
Homicide detectives from the Met’s Specialist Crime Command are investigating and enquiries remain ongoing.