Footscray factory fire triggers smoke warning across Melbourne's ...

More than 20 fire trucks were called to battle a fire at the old Kinnears factory site in Footscray on Wednesday night.

In 2017, three people died in a deliberately lit fire at the site.

An investigation is underway into the cause of last night's blaze, but fire authorities have not deemed it suspicious at this time.

An investigation is underway into a fire on Wednesday night at the old Kinnears factory, in Melbourne's west, where three people died in a fire in 2017.

Authorities responded to the blaze at the factory in Ballarat Road, in Footscray, about 7:45pm after multiple calls to triple-0.

More than 20 firefighting vehicles attended the blaze, which was brought under control in less than an hour.

Fire Rescue Victoria's Tony Milczakowsky said there was a partial roof collapse and sections of the building were heavily impacted by flames.

"We did escalate the response once we got on scene because it was quite a large fire," he said.

"It took us about half an hour to bring it under control. At the height of the blaze [there were] approximately 20 appliances and about 80 crew members." 

Mr Milczakowsky said there was an order to eventually knock down the building, but for the time being demolition crews were securing the area to make it safe.

He said fire investigation crews were working to understand how the fire started, but were "not looking at any suspicious circumstances at this time".

There were no reports of injury.

Fire engulfed the old Kinnears factory site in Footscray on Wednesday night.(ABC News)

A Watch and Act alert was issued about 8pm on Wednesday for Footscray, urging residents in the surrounding area to avoid Ballarat Road and stay indoors.

Authorities said people should close their doors and windows, turn off heating and cooling, close fireplaces and vents.

Ballarat Road was also closed, with authorities hoping to reopen it by the end of the day. 

Footscray resident Kominos Zervos said he was concerned the fire could have done significant damage to the factory, which dates to the early 1900s.

"I'm worried about the safety of the brick outer structure that is still standing," he said.

More than 20 fire trucks were called to the factory in Ballarat Road.(ABC News)

Three people died at the factory in 2017 in a deliberately lit fire.

The site has been earmarked for development for a number of years.

Wednesday's blaze follows a large chemical explosion in Melbourne's west earlier this month, which resulted in one of the state's biggest fires in recent years.

Colleen Hartland from the Anti-Toxic Waste Alliance said the frequency of factory fires was a cause for concern.

"I've gone through quite a few of these and your stomach turns every time you hear more than two fire engines go past past your house because you know it is probably going to be something terrible," she said.

"This is our third major fire in the west in a month so something's going badly wrong in terms of inspections on these sites."