Around 100 firefighters are battling a large factory fire in Sydney's southwest.


Emergency services were called to Governor Macquarie Road in Chipping Norton at 3.30am on Sunday following reports of a factory well alight.


Firefighters worked for several hours to contain the blaze amid fears it would spread to several adjoining factories, Fire and Rescue NSW spokesman Ian Krimmer said.


He said the blaze at the "large" factory, which was believed to be an automotive business, has been contained but it could take a whole day before it is completely extinguished.


"There's a lot of tyres and plastics still burning so it could take some time before it's fully doused," Superintendent Krimmer said.


The fire has also created a large plume of smoke in the industrial area and authorities are monitoring the atmosphere around the building.


Governor Macquarie Road has been closed.


AAP