A woman has been found dead and a man is in custody after a house fire in Perth’s southern suburbs, with police declaring the incident a murder.

Firefighters were called to the Warnbro home in the early hours of Friday morning, where the body of a 30-year-old woman was discovered.

Paramedics took two other occupants of the home, a 35-year-old man and a three-year-old girl, to Rockingham Hospital for treatment of smoke inhalation.

Acting Detective Superintendent David Gorton said homicide detectives were treating the suspicious death as a murder.

A man in his 30s, who was known to the woman, is in custody assisting police.

“Any death is a tragic event but when people are murdered it does have a lasting impact on family, friends and the broader community,” Det Supt Gorton said.

The home sustained minimal damage in the blaze.

–AAP