Factory fire smoke blankets Melbourne's southwest

Smoke from a massive factory fire in Melbourne's southwest is billowing over surrounding suburbs as authorities urge residents to shut their doors and windows.

Firefighters were called to the blaze, at a garden supplies factory in Altona North, just before 8pm (AEDT) last night, Metropolitan Fire Brigade communications controller Keith Robinson said.

It took about 80 firefighters more than an hour to bring the blaze under control and some stayed throughout the night to continue mopping up.

The factory is believed to contain fertiliser ingredients, and the collapse of parts of the building has made conditions difficult for firefighters.

"There appears to be a high fire load and the building collapse makes it hard to get water into the right spots," Mr Robinson said.

No one was injured in the blaze but the building suffered severe structural damage.

Large plumes of smoke clouded the sky and travelled in a south-westerly direction, with residents urged to shelter inside from the smoke and keep all doors and windows closed.

Fire authorities also issued a watch and act warning for residents in Yarraville, Brooklyn, Braybrook and several other surrounding suburbs at 10.30pm.

Investigators are expected to attend the scene this morning to establish a cause for the fire, which is believed to have caused $1 million in damage.

Police also attended the scene and urged all residents in the surrounding suburbs of Altona North, Newport and Brooklyn to ensure they stay indoors and.