A fragment of ammunition was removed from the thigh of a 59-year-old woman yesterday after it had remained undetected for almost four decades.
Police are still investigating whether the rusty piece of metal, about 3cm long, is a bullet or part of a cartridge.
The woman told police that she had been injured while working in a mainland coal factory about 40 years ago.
She said her left thigh was hit by a hard object when the wheel of a cart she was pushing ran over something.
The fragment was found only after she went to the Caritas Medical Centre in Cheung Sha Wan on Thursday complaining of pain and swelling in her left thigh.
"She told police that she did not receive proper medical treatment to treat her injuries and she did not realise the fragment had remained in her leg," a police officer said.
The piece of metal was removed in an operation and the hospital alerted police to its nature at about 1.45pm yesterday. The fragment has since been taken to the police forensic firearms examination bureau for testing.
The woman was recovering in hospital last night.
A police spokeswoman said the case was being treated as "ammunition found".
Crime squad officers from Sham Shui Po police have been assigned to investigate the matter.
Surgeon Dr Tjiu Cheung-sun said that medically, it could be dangerous for an object to stay in a person's body for such a long time, because there was a risk of infection.
"It's definitely a rare case, but it's still possible that the patient failed to notice it for such a long time," he said.