The girl, who was given the temporary name of Elsa, was discovered in Newham on Thursday last week by a dog walker who kept her warm with blankets until paramedics arrived.

She was found wrapped in a towel inside a reusable shopping bag near the junction between the Greenway footpath and High Street South at around 9.15pm.

The Metropolitan Police said a woman was seen entering the Greenway from the busy road 30 minutes earlier at around 8.45pm. They believe she later left the footpath and headed towards Fabian Street.

The force described the woman as black and said she was wearing a large dark coat with a light-coloured scarf or hood. She also had a rucksack on her back.

Police are also looking to identify a witness, believed to be a man, who might have seen the woman in the vicinity.

Officers said he was wearing a dark-coloured hooded coat and a backpack. The coat or backpack also had a reflective strip on the back.

"If you have information about these people - or you think I might be describing you - I urge you to please, please contact us immediately," said Chief Superintendent Simon Crick, lead for policing in Newham.

"It could turn out that you have nothing to do with it but, it's still incredibly helpful for us to know so we can focus our efforts on other avenues instead."

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Ch Supt Crick said there had been 17 reports from members of the public sharing information.

He added: "Baby Elsa is safe and well.

"I'm sure people will have seen recent reporting that she has now left hospital. Our colleagues in Newham Council continue to make sure she's well looked after and cared for."

Ch Supt Crick said the force had collected "a considerable volume of CCTV footage" but said officers were "still examining it in detail".

He added: "I want to appeal directly again to Baby Elsa's mother.

"Your daughter is safe and well, but we need to make sure that you are too. You might need urgent medical care and support, and we can help you."