A teenage girl was gunned down in the street with two friends while clutching her 11-month-old son in her arms.
Jessica Chrichlow, 18, collapsed to the ground alongside two sisters - named locally as Sammy, 17, and Alex, 19 - after being caught in the crossfire of a botched gangland attack, witnesses said.
Police said it was "hugely fortunate" that the baby escaped injury.
Detective Chief Inspector Mick Foote said: "It was a random, reckless act and we are fortunate we are not dealing with a fatal shooting here."
The three victims had been outside in John Fearon Walk, North Kensington, west London, enjoying balmy temperatures when the attacker got off a bike and screamed "mother f****r" at the group, a neighbour, who did not want to be named, said.
Police said the child may have been missed by inches as the bullet hit his mother.
Mr Foote added: "I do not believe the girls were the intended targets. What's particularly devastating is that the young girl was carrying a young child.
"This was totally unprovoked."
As a hunt was launched for several young men seen on bicycles on the west London housing estate last night, the officer said he was "working on the basis" that the shooting was gang-related.
One neighbour said her 12-year-old daughter saw the shooting from her bedroom window.
Jacky Cinesey said: "I have sent her to school in tears today.
"These girls were just outside enjoying the sunshine. It's horrifying."
The girls had been enjoying the weather in a back garden when they began talking to a "large group" of boys outside, Mr Foote said.
"It appears that a man on his own has gone towards the crowds and discharged a single shot from a shotgun," he said.
The gunman fled the scene and joined three other hooded males on bicycles, he added.
Miss Chrichlow's mother Isabel, who lives nearby, spoke only to confirm her daughter had been shot.
Another local, Jenny Kantinda, 30, said she knew the three victims.
"They were just sweet girls, we have had enough," she said.
"The gang trouble has gotten worse, it's time police did something to help us.
"There are young children living here - are they safe? I don't think so."
Ms Cinesey, 36, said her daughter - who she did not want to name - had seen the gunman just "stand and stare" at the victims after the shooting.
She added: "Another woman then appeared outside with a pram. It could have been even worse."
Neighbour Leslie Arandi, 55, added: "The gangs are always cycling around here smoking drugs. I'm fed up with it. Hopefully now the authorities will take notice."
Sammy has been discharged from hospital while the other two victims remain in a stable condition.
The investigation is being led by Trident detectives, who deal with gang crime in the black community.
A police spokesman said officers were alerted by the ambulance service at 7.17pm yesterday after calls from members of the public.
Karen Buck, MP for Westminster North, expressed her concern as she visited the troubled Mozart Estate where the attack took place.
The Labour politician, who has previously called for crackdowns on knife and gun crime, tweeted: "Desperately worried about local gang and youth violence. We have to get a grip."
Community leaders have made several attempts to make the area safer in recent years.
Yew trees and a herb garden in a chequerboard pattern were planted along John Fearon Walk after it was identified as a hotspot for anti-social behaviour.