Witnesses have described a "horrific" scene after a mother and her two girls were doused in their car with a "corrosive substance" in south London.
One witness told the BBC the mother cried: "I can't see, I can't see" as he tried to help. "It was quite horrific," he added.
The Metropolitan Police said injuries to the mother and the younger girl, three, could be "life-changing".
The attack is believed to be targeted.
Police said an alkaline substance was used in the attack, which happened on Lessar Avenue, near Clapham Common on Wednesday evening.
Shannon, who lives on the street, said she ran outside after hearing "a lot of shouting" then a "bang" and "someone saying 'help'".
"As I run outside, I've seen this guy throwing a child on the floor, he picked her up and threw her again."
Shannon said she ran over and grabbed the child, carrying her to safety in her block of flats.
"I've then seen her mum walking up the road saying 'I can't see I can't see'."
At that point her partner set off after the suspect.
"I chased him halfway down the road, but I was in slippers so didn't get very far," her partner told the BBC.
"As I came back, that's when I saw the woman who had been attacked ... so I ran inside to get some water and just sprayed her down with water."
He described seeing what looked to be serious burns to her face.
Shannon, who suffered less serious burns to her face, arm and lips after caring for one of the children involved, was taken to hospital but later discharged.
"My skin started tingling as well, my face started tingling," she said.
A resident named Abdul said he saw baby's shoes on the street as he was returning home from a dentist appointment.
"People were just screaming everywhere, there were fifteen police cars and fire brigades, it was quite a stressful moment."
"It was so shocking that it would happen right next to my house."
He said police often patrol the street.
Another resident, who told the BBC his name was David, witnessed the aftermath of the incident.
"The people on the street [are] fearful. This is a safe neighbourhood, so this is shocking," he said.
As the search for the attacker began, residents said they heard the whir of helicopters through the night.
The nature of the attack has left residents distressed. "How can people do this sort of thing?" one neighbour asked.
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