Melbourne factory fire 'suspicious'

A factory fire that forced the evacuation of homes in Melbourne is being treated as suspicious.

It took firefighters almost two hours to put out the blaze in the abandoned building in Brunswick on Friday morning.

Flames and heavy smoke forced firefighters to evacuate nearby residential units, which were earlier under threat from the blaze, while Sydney Road was shut down near Albert street because of smoke.

An MFB spokesman said firefighters had difficulty accessing the fire because of structural issues with the building.

"We're gaining access by using both the aerial appliances squirting water through the roof and we're also accessing with firefighters at ground level," he told reporters.

Firefighters are expected to be on the scene for several hours, and potentially into the evening, to ensure no flare-ups.

Residents and nearby shopkeepers have been allowed to return home and to work.

Police are now investigating the cause.