Firefighters are yet to bring a blaze in a Melbourne supermarket under control, more than two hours after the alarm was raised.

Thick black smoke billowing from the Little Saigon Market in Footscray has forced road closures and prompted a warning to residents to close doors and windows and turn off airconditioners.

The MFB were called to the Nicholson St complex shortly after 6am local time.

More than 60 firefighters, three ladder platforms, two ultra-large pumpers and 12 pumpers are at the scene, still trying to bring the fire under control.

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"It appears the fire began in the cool room area of the premises and quickly took hold, engulfing the building," the MFB says in a statement.

"It's believed no one was inside at the time."

The blaze is forcing road closures and smoke is affecting driver visibility during the morning peak hour.

Nicholson St Ryan St, Leeds St, Donald St and Byron St are all closed and trams have been stopped at Droop St.

- AAP