The fire at the old Alcoa plant near Geelong. Photo: Supplied

Dozens of firefighters have battled a blaze at the Alcoa plant near Geelong that forced the evacuation of about 30 workers on Wednesday.

Firefighters were called to the decommissioned aluminium smelter on Point Henry Road in the industrial suburb of Moolap about 3.30pm.

CFA District 7 duty officer Wayne Aylmer said the fire broke out in a section of the old rolling mill that is being disassembled.

He said about 30 workers were safely evacuated and the fire was brought under control at 4.20pm.

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"There is a significant amount of smoke in the area which is expected to remain for some time," Mr Aylmer said. "I want to reassure residents there is no risk to the community."

An advice message was issued earlier due to the amount of smoke coming from the building. The CFA said the blaze did not threaten any other property but people are being told to avoid the area.

Alcoa closed down its Point Henry smelter and rolling mill in 2014, more than 50 years after opening.