Fire crews  knocked out the blaze on Alderson Place at 1:30pm, with three trucks, a HAZMAT unit as well as the aerial firefighting appliance on scene.

They cut holes in the roof of the building for ventilation, and fire crews battled the blaze from the outside.

ACT fire commander Michael Cochrane expected firefighters to be at the factory all night after first responding at about 11am.

"There seems to be a fairly high fuel load inside the structure," Mr Cochrane said.

Earlier, Mr Cochrane had pulled out crews inside the building over concerns of those high fuel loads, but by 1pm fire crews had re-entered.

Bystander Hugh Mckenzie and his mum, Louise McKenzie, saw a man trying to fight the fire with a garden hose.

"He walked out of the back there and he just sort of laid down and then he got back up again. Everyone went down to help him," Mr McKenzie said.

"I haven't really seen anything like that before."

The man was seen to sit up, before laughing with the firefighters and paramedics as they treated him.

He stood up and walked with paramedics, and people who appeared to be family or friends, to an ambulance.

Emergency services confirmed the man had a cardiac episode before he collapsed but was being treated at the Canberra Hospital.

Smoke is visible in several nearby suburbs, including over the border in Jerrabomberra and Queanbeyan.

An emergency services agency spokesman said firefighters had protected the perimeter of the property to ensure the fire didn’t spread to adjoining buildings.

"ACT Fire and Rescue HAZMAT specialists are monitoring the air quality."

The ACT health directorate warned that people with respiratory conditions should avoid exercise and stay indoors if affected by the smoke.

"People with asthma in particular should continue their medication and consult their general practitioner if they have any difficulties," a spokeswoman said.

The Emergency Services Agency said it received reports of the fire about 11.07am.