Firefighters are still working to bring the fire under control in the building which measures 30 metres by 40 metres.
Firefighting operations were interrupted earlier this morning because of multiple explosions from inside the premises.
The suburb of Mitchell remains evacuated due to concerns over the possibility of toxins in the smoke from the fire. Police are operating road blocks on all entrances to Mitchell. People should avoid the area until further notice.
Evacuation centres has been established at Canberra Stadium and Dickson College.
An EMERGENCY ALERT telephone advice has been issued for residents within a 10 kilometre radius to remain indoors until further notice.
People are urged not to ring 000 unless for a life threatening emergencies. All telephone inquiries should be made to Canberra Connect on 13 22 81.