A fire which engulfed an inner Brisbane apartment complex started by accident, an early investigation has found.
Four people, including an unconscious woman, were rescued after fire engulfed the Fortitude Valley complex late on Sunday afternoon.
The woman remains in Royal Brisbane and Women's Hospital.
Adam Pearson, the assistant caretaker of the Cathedral Place complex in the Fortitude Valley, said six to eight top floor units in block H were burnt, while the rest of the building down to the ground floor suffered extensive water damage from fire extinguishers.
"There are sections of roof missing and flooring collapsing," he told AAP.
"It's quite extensively damaged."
Smoke caused electrical damage to neighbouring block G, while residents in the remaining six blocks of the complex were allowed back in on Monday morning.
Residents told journalists that a drug lab explosion caused the blaze but a joint investigation by police and Queensland Fire and Rescue has confirmed it was an accident.
"There are no suspicious circumstances," the Department of Community Safety said in a statement, without explaining the cause.
Earlier, Police Minister Jack Dempsey doused suggestions that illegal activity caused the fire.
"There's a number of unfactual reports that are not based on sound evidence at the moment," he told reporters.
"I look forward to the forensic reporting and the report by the police service, which will be coming out in the next 24 hours."
The 14-year old complex where the fire occurred is home to 1600 people and contains 514 units.
It is not known at this stage how many people were evacuated and remain homeless.
"At some point, they will be allowing residents to retrieve essentials but as for when, we have no way of knowing," Mr Pearson said, adding it could be some months until some residents in block H could move back in.