A man has been found dead in his northern NSW home.

Family members of the 46-year-old called police to an address at Narrabri around 9.55am (AEDT) on Wednesday after finding his body.

The man, whom police have been told lived alone at the address, had suffered significant injuries.

A crime scene was established and forensic specialists are investigating.

The investigation comes as police probe the discoveries of two men found dead in separate western Sydney locations on Thursday.

One of the men, a factory employee found in Dunheved who had been knifed, is believed to have been attacked by someone he knew.

The other death, of a man found at an oval in Fairfield, is also being treated as suspicious.