Illegally stockpiled containers of chemicals are slowly being removed from eight sites in Epping and Campbellfield.
A WorkSafe-led taskforce began removing the chemicals on Wednesday, taking containers from one of the Epping sites.
The taskforce, which also includes Environment Protection Agency and fire services, will test the containers before loading them onto trucks designed to transport dangerous goods.
The chemicals will be taken to licensed storage facilities for assessment before being recycled of destroyed.
The chemicals were discovered in late December when EPA, WorkSafe and fire services inspected a number of sites in the northern suburbs as part of an investigation into a Tottemham industrial fire in August.
It will likely take a number of weeks to clear all eight sites.
In a statement, WorkSafe said atmospheric monitoring would be conducted inside and outside each site, while fire prevention and security measures were also in place.
Investigations into the circumstances that led to the chemicals being stored at the sites are continuing.