A dog walker has found an ice cream tub containing what appears to be human placenta, police say.
Scotland Yard said the find was made on a footpath near Tooting Bec Athletics Track, south London, early yesterday morning.
Medical staff examined photographs and suggest it is human placenta, possibly a fortnight old.
Police say they are now concerned a vulnerable woman has given birth and may require medical assistance.
Police believe the tub was partially buried, but later dug up by an animal. It has been sent for pathological examination.
Police sniffer dogs could not find anything else.
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."
Police appealed to anyone who uses the path at the back of Tooting Bec Athletics Track to contact them if they have recently seen anything there which was out of the ordinary.