The body of a newborn baby girl has been discovered in undergrowth close to a footpath.
Detectives expressed concern for the welfare of the baby's mother after the child was found wrapped in a black bin liner.
The baby was discovered by passers-by near a footpath by the Ingrebourne river in Rainham, Essex.
Police launched a search for the girl's mother after the child was discovered at 4.40pm on Sunday.
Officers said the baby was found off the A1306 New Road with a "distinctive" Primark vest which is not sold in the UK.
Post-mortem examinations are being held held at Great Ormond Street Hospital to establish a cause of death.
Despite carrying out extensive inquiries, detectives have been unable to trace the mother. They are concerned that she may need medical attention.
Detective Inspector Colin Welsh said: "The baby was newborn and we are concerned that the mother might need urgent medical attention.
"I would appeal to anyone with information to contact us. The vest inside the bin liner is quite distinctive and I am hoping that someone might recognise it."
Officers would also like to hear from anyone who might have seen the bag being left in the undergrowth which they believe could have been some weeks ago.