A fourth bone has been located on Port Macquarie's Flynns Beach.
A passers-by found the bone on Sunday (July 14) afternoon.
The small bone is believed to be human, police said.
Police confirmed the bone will be subject to forensic examination, with any results being compared with missing persons records.
The bone was discovered in the vicinity of Flynns Beach.
In June, spear fishers uncovered a total of three human bones at two beaches in the vicinity of Flynns Beach.
On June 15, divers located one bone in the waters off Flynns Beach. The bone was handed into Port Macquarie Police Station.
Following the discovery of the first bone, Mid North Coast Police commenced a search operation at the beach with the assistance of Sydney police divers on Sunday, June 16. No further items were located.
On Monday, June 17, officers from Port Macquarie Police District were advised that another two bones had been located in the waters around Flat Rock, east of Nobby Head, by another spear fisherman.
Police are continuing their investigations.
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