Australian police said on Sunday they expect to charge a 31-year-old woman with arson after she allegedly set fire to the Covid-19 quarantine hotel where she and her two children were staying.

No one was injured in the fire, which gutted much of the 11th floor of the Pacific Hotel Cairns, police said. More than 100 people were evacuated from the hotel.

The incident in the northern city of Cairns occurred as tensions rose in parts of Australia as a result of coronavirus restrictions and the latest scare caused by the emergence of the Omicron variant, first identified in Southern Africa.

Acting Chief Superintendent Chris Hodgman said the woman was in custody and police were caring for her children.

"I expect later on this morning that the 31-year-old female will be charged with arson and the possibility of other offences," he told reporters.

The woman had been in quarantine for a couple of days and there had been issues with her that authorities "were managing", Hodgman said.