The 47-year-old died after being rushed to hospital following the blaze in Ayr, about 5.40am on Tuesday.

Her 65-year-old partner was also taken to hospital in critical condition after suffering burns, while a second man in his 20s also received treatment.

Investigators have been unable to speak to the 65-year-old, who continues to receive medical treatment, but say the woman's death is being treated as a homicide.

Acting Chief Superintendent Chris Lawson confirmed the couple had been in a relationship and a current domestic violence order had been in place since 2018.

Detectives and firefighters are investigating the cause of the blaze but believe the woman died before the fire was started.

A second investigation is under way after police and emergency services had been called to a mental health incident at the home hours before the murder.

Police and ambulance officers spoke to all parties involved at the time and left shortly after, with the actions of the officers under review by the ethical standard commend and the CCC.

"The welfare check remains under investigation," Supt Lawson said.

"It's not a great result and that's why we have the ethical standards command and the CCC overviewing the investigation into that initial interaction with the couple."

Australian Associated Press