A man has been arrested after his partner and her six-year-old son were found dead at a house in Bolton-le-Sands, near Lancaster.
Police were called to the property in the Lancashire village and found the bodies of a woman and a boy.
The 36-year-old man, who was found with what were thought to be self-inflicted knife wounds, was airlifted to the Royal Preston Hospital and arrested on suspicion of murder.
The suspect was described as being in a serious condition.
Post-mortems are set to be carried out on the bodies of the woman and child. No further details of the victims have been released.
Det Supt Paul Withers said: "We are still in the very early stages of this investigation but we are conducting a number of inquiries in order to establish the exact circumstances surrounding the deaths.
"This is being treated as a murder inquiry."
Anybody with any information should contact police on 101 or Crimestoppers anonymously on 0800 555 111 or on-line at Crimestoppers-uk.org.