A 15-year-old boy has been stabbed to death near Stratford Shopping Centre.
Officers found Baptista Adjei critically injured on Stratford Broadway, east London, shortly after 15:20 BST on Thursday.
Police believe he was either attacked on a bus, or shortly after getting off.
A 15-year-old friend of Baptista, who had been travelling with him, was also stabbed and remains in hospital with non life-threatening injuries. Scotland Yard said no arrests had been made.
Det Ch Insp Chris Soole said the boy was stabbed during a fight "on or shortly after alighting from a bus which stopped very close to Stratford Shopping Centre".
He added: "The victim of this stabbing was a schoolboy with his whole life ahead of him. He had everything to live for.
"This was a senseless attack and we share the concern and alarm this murder will no doubt cause in the local community."
In a separate stabbing about five hours later, an 18-year-old man was knifed to death in south London.
Police found the man suffering from stab injuries on the Brandon Estate in Camberwell, at about 20:20 BST.
He died at the scene an hour later and no arrests have been made.
Baptista's friends and members of the public provided first aid but he died at the scene at about 15:50, police said.
The teenager's next of kin have been informed, and the second boy who was stabbed remains in an east London hospital.
At the scene
By Greg McKenzie, BBC London
There is a huge crime scene around the Stratford Centre following the boy's death.
A blue and white tent remains in place, marking the spot where he was confirmed dead.
Many children are heading through the area on their way to school and are seeing this crime scene. Some are taking photos, others are in tears.
There's another police cordon across the road where the other 15-year-old boy was stabbed, while another cordon is in place at the nearby church as police continue to investigate.
A Section 60 order was implemented, giving officers increased stop and search powers across Newham.
Police have closed off a large part of Broadway, and the shopping centre entrance nearest Stratford Station has also been closed.
One witness, who did not want to be identified, said the attack happened outside a McDonald's.
"At that moment there were not many people around him so I could see him all covered in blood. He was in pain and tried getting up," they said.
"There were people around gathering. It was scary as you did not know if any of them could have had a knife too."
Mayor of London Sadiq Khan said he was "utterly devastated" to hear about the two killings.
Devastated to hear that two young Londoners have lost their lives to violent crime. My condolences to the loved ones of the victims at this extremely tough time.— Sadiq Khan (@SadiqKhan) October 11, 2019
If you have information about these crimes, I urge you to contact the police on 101 or @CrimestoppersUK anonymously. pic.twitter.com/UUB2obxfxZ
There have been more than 110 homicides in the capital this year, with about 70 of those being fatal stabbings.