The three bodies were discovered in St Johns Park in Sydney's west. A 44-year-old man has been arrested after he was taken to Liverpool Hospital with unspecified injuries.
Police and paramedics were called to the ground floor apartment at 7am (AEST) today and made the arrest shortly after.
Fairfield Local Area Commander Peter Lennon was unable to confirm reports the victims were believed to be a mother, father and their son.
The victims are yet to be formally identified.
Two dead dogs were also found at the scene.
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Superintendent Peter Lennon says there was a lot of blood inside the apartment
with the three bodies found together in the unit's main bedroom, two on the bed and another nearby.
Supt Lennon says it's too soon to say how the three people died, with the address not known to police and no apparent motive clear. He also said that no weapon had been found.
He says the identification and relationship of the people is
still being investigated.
The triple-0 call that drove police to the scene was made by a man whose identity is not known.
Fairfield police are investigating with the homicide squad and a report will be prepared for the coroner.
