A woman and her two young daughters had a corrosive substance thrown on them in London, where they were receiving treatment at a hospital Thursday, police said.

The city’s Metropolitan Police force said officers received reports that a man pushed a 3-year-old girl to the ground and threw an alkaline substance at her, her 8-year-old sister and the girls’ 31-year-old mother near Clapham Common, a residential area in south London, on Wednesday evening.

The woman and the 3-year-old girl suffered potentially life-changing injuries, the police department said. Officers were searching for the assailant, whom investigators think was not a stranger to the woman.

“We believe the man and woman are known to each other. Our investigation is in its early stages and we are working to establish why this awful incident has happened,” said superintendent Gabriel Cameron.

“While this appears a targeted attack, he is a dangerous individual and we urgently need to find him,” he added.

Police said the suspect fled on foot after he crashed into a stationary vehicle in his attempt to drive away from the scene.

Three members of the public who tried to help the family were treated for minor chemical burns. Five police officers also went to the hospital because of contact with the substance, but only the woman and her children remained hospitalized Thursday.

One witness, Shannon Christi, said she helped pull the 3-year-old victim away from the scene after she saw a man throw the child on the ground. She also said she saw the mother saying, “I can’t see.”

“My skin started tingling as well, and my face started tingling,” Christi said. “It all happened so fast.”

Metropolitan Police chief Mark Rowley called the incident “ghastly” but added that attacks involving acids and chemicals were “exceedingly rare” in the British capital.

(AP)