Just before 5pm on Thursday, officers received a report of human tissue being found by a passer-by at Werneth Park on Frederick Street.
Officers have been carrying out a number of enquiries and examining the scene and are now appealing for anyone with information to come forward as there are concerns for the welfare of the woman.
Detective Inspector Rachel Smith, from GMP's Oldham CID, said: "Since receiving the report, we have been carrying out a number of lines of enquiry but our priority to find the woman and make sure she is safe and well.
"She may be in need of urgent medical attention and she is our absolute priority at the moment.
"Anyone with information or may have seen a woman in distress is asked to call us on 0161 856 8919 quoting incident number 1983 of 24/06/21.
"Information can also be reported online or by using our LiveChat service at www.gmp.police.uk.
"Alternatively, contact Crimestoppers anonymously on 0800 555 111.
"We would ask that people don't speculate on the circumstances of this discovery as it hinders our investigation and is upsetting for those involved."
