Police were called to the carpark of the fast food outlet on Queen Street at Campbelltown around 5:30am today, following reports of a stabbing.
There a male NSW Ambulance paramedic was treated at the scene and was transported to Liverpool Hospital.
His condition is not yet known.
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Police arrested a man and have taken him to Campbelltown Police Station for questioning.
A crime scene has been established, which will be forensically examined by specialist officers. Members of the public are urged to avoid the area.
Officers from Campbelltown Police Area Command are investigating the circumstances surrounding the incident and anyone with information is urged to come forward.