About 30 firetrucks and 80 firefighters are on scene at the Epping blaze, which has been burning by the intersection of High and Cooper streets since about 5am.
The fire was brought under control about 8am.
Emergency services have closed parts of High Street and erected road blocks as they battle to control the fire, causing a significant traffic build up ahead of peak hour.
Drivers and commuters are being told to use Edgar or Dalton Road instead.
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An advice message has been issued alerting the local community to the large amount of thick smoke in the area, but authorities have said the smoke is not toxic.
People are being advised to close their windows and turn off air conditioning units.
A Supercheap Auto store has been seen at the centre of the flames.
It has ended up caved in from damage, while a Cash Converters store next to it has also been burnt.