The bodies of three children and a man have been found at a property in Staines, Surrey Police have said.
Officers were called by the ambulance service to the address in Bremer Road at about 13:15 BST on Saturday.
Chief Inspector Lucy Sanders said: “We are working to establish exactly what has occurred.”
She said the next-of-kin of those who died were aware and being supported by specialist officers.
At this stage, police believe it to be an isolated incident with no third-party involvement, she said.
Bremer Road is currently closed while investigations are carried out.
Ms Sanders said: “This is a tragic loss of life in our community and we are working to establish exactly what has occurred.
“There is currently a significant police presence at the location, and in the surrounding area, and we would like to thank local residents for their patience and understanding whilst we conduct our investigation.”
She said Surrey Police had completed a mandatory referral to the Independent Office for Police Conduct, because of previous police contact with those involved.
