The family of a woman who was tied to a chair, doused in flammable liquid and set alight is believed to be flying to Perth from China to be by her hospital bed.

The 29-year-old woman remains in an induced coma in Royal Perth Hospital's intensive care unit after suffering burns to 60 per cent of her body.

The Chinese woman, who is an Australian citizen, was discovered after firefighters were called to a burning unit in the southeast suburb of Cannington about 11.30am (WST) on Wednesday.

WA Police Commissioner Karl O'Callaghan told reporters on Thursday the woman was in a critical condition.

Mr O'Callaghan said a 31-year-old man was released without charge on Thursday morning after police questioned him for several hours overnight.

"We have interviewed somebody this morning - a person of interest - and that person has been released," he said.

"No charges have been laid as yet."

The woman, who had been working in a Perth office after graduating as an overseas student and gaining Australian residency, was put in an induced coma after undergoing surgery on Thursday.

"The next three to five days will be crucial," a police spokesman told AAP.

Police at the scene on Wednesday said the unit complex where the woman was staying was mainly occupied by overseas students.