A newborn girl was discovered in East London wrapped in a towel inside a shopping bag, as per the authorities.
A member of the public found the baby in Newham, and she was kept warm until paramedics came.
She was not hurt in any way, according to the Met Police, and is doing well at the hospital.
The force appealed for the baby’s mother to get in touch and said “Please know that your daughter is well, no matter what your circumstances, please do seek help by dialing 999”.
A dog walker discovered the infant at the intersection of Greenway and High Street South on Thursday at around 21:15 GMT, prompting police to be summoned.
The walker’s efforts to keep the young child warm “contributed to saving the baby’s life,” according to Ch Supt Simon Crick.
He said, “Our thoughts now turn to the baby’s mother; we are extremely concerned for her welfare as she will have been through a traumatic ordeal and will need immediate medical attention following the birth.
“Trained medics and specialist officers are ready to support her and we urge her to get in touch by phone or walk into the nearest hospital or police station.”
Also, the force is requesting that anyone who believes they know the mother get in touch with them.