An ice cream tub believed to contain human placenta has been found by a dog walker.
The discovery was made on a footpath near Tooting Bec Athletics Track, south London, at about 6.55am, Scotland Yard said.
The dog walker initially thought they had found a human organ in the container, which police believe was partially buried before being unearthed by an animal.
Medical staff who examined photographs of the substance have suggested it is human placenta which could be two weeks old.
The item has been taken for pathological examination.
A search using specially trained police "blood" dogs did not find any other items buried in the area, the Met added.
Police said the early indication of human placenta has raised concerns there may be a vulnerable new mother who has given birth and may require medical assistance.
Chief Inspector Nick Aldworth said: "Obviously we are at the very early stages of the investigation into what has been found, but the suggestion that it could be a human placenta does give us concern that there could be an individual whose health and wellbeing may be at risk.
"That said, we retain an open mind regarding the item and how it came to be buried on the pathway pending the results of testing and any confirmed information coming to light.
"Therefore we are appealing to the person who buried the item to contact us, or anyone who knows the person who buried the item. Your call will be treated in the strictest of confidence.
"We are also appealing to anyone who uses the path at the back of Tooting Bec Athletics Track to contact us if they remember seeing anything out of the ordinary there recently.
"I would like to emphasise that our primary concern at the moment is for the welfare of anybody who may have given birth without medical assistance and our focus is currently on welfare and not enforcement. Anybody who comes forward will be treated with this in mind."
Anyone who can assist police is asked to call on 101.