SES volunteers are on scene at the toilet block at John Breen Park searching for evidence.
Meanwhile police said they are investigating two assaults in the North Mackay area overnight which detectives believe may be linked.
About 7.50pm, police were called to an address on Daniel St, Mount Pleasant after a 23-year-old man was located with lacerations to his face.
Further investigations have led police to an address on Harris St in Beaconsfield where a 27-year-old man was discovered unconscious with head injuries.
Both men have been taken to the Mackay Base Hospital for treatment, and the 27-year-old has been flown to Townsville for surgery.
Police have established a number of crime scenes, and investigations are continuing.
A QAS spokeswoman said a man was taken to Mackay Base Hospital in a stable condition after a reported stabbing from Harris St in Beaconsfield about 8.20pm last night.
The spokeswoman said another man in his early 20s with cuts to his face was also taken to hospital about 7.53pm from Daniel St, Mount Pleasant in relation to another reported stabbing.
More to come.
A crime scene has been established at John Breen Park in North Mackay this morning, Mackay District Duty Officer Dave Parnell said.
He said an investigation is underway by CIB into the incident that occurred overnight.
The toilet block at the park has been cordoned off as investigations continue.
A police media spokesman said they are still trying to determine what happened.
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