Emergency crews were called to the Hubert Street property about 4.30pm on Wednesday following reports of a building in flames, with smoke blanketing the entire CBD.
Surrounding roads, including Gibbon, Stanley, Raid and Hawthorne streets, have been closed with police making an emergency declaration under the Public Safety Preservation Act.
A man was transported to the Royal Brisbane and Women's Hospital suffering from life threatening airway burns, a Queensland Ambulance Service spokeswoman said.
No one else has been hospitalised but four ambulances remain on standby at the scene.
Fire crews are using a ladder platform to get better access to the blaze. (HANDOUT/NINE NEWS QUEENSLAND)
About 15 fire crews remain on scene, fighting the blaze  which continued to burn "quite big", a Queensland Fire and Emergency Service spokesman said.
Resources included a ladder platform allowing firefighters to access the flames from a very high level.
Crews have not entered the building with nearby structures also under threat.
Members of the public have been advised to avoid the area and those within the exclusion zone asked to remain indoors until further notice.
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