A suspicious fire has ripped through a factory near Melbourne Airport, destroying a building and sparking a health alert for locals.
Police believe a car was driven into the premises at Tullamarine, in the city's northwest, and set alight around 3.30am on Thursday.
The building was completely alight when 80 firefighters arrived.
Crews managed to stop flames destroying nearby businesses at the industrial park on Barrie Road.
No one was inside the building at the time and there were no reports of injuries.
Fire Rescue Victoria Commander and Incident Controller John Zuccarelli said a car detailing business operated from the factory.
Crews were initially unable to enter the building due to the risk of the structure collapsing, so he could not reveal what was stored inside.
"The damage is quite extensive and it be won't be salvageable," Mr Zuccarelli said.
Gas and electricity to the site were switched off during the fire fight, with nearby power lines posing a danger.
The blaze sparked a health alert for smoke for residents living up to two kilometres away and locals were told to avoid the area.
An arson chemist was investigating what took place and a crime scene was set up.
While motorists were urged to avoid the area, the incident had no impact on operations at nearby Tullamarine Airprt.
The fire is being probed by local investigators and not Taskforce Lunar, a specialist squad investigating more than 100 firebombings linked to conflict between crime gangs over the profits of illegal tobacco.
