Firefighters have worked through the night to control a fire that sent massive plumes of black smoke billowing over Queanbeyan as a scrap metal yard in the industrial suburb of Beard went up in flames.
Those living in Queanbeyan West, Jerrabomberra, Karabar and Harman were told to stay indoors and close their windows on Sunday night by the Emergency Services Agency.
Firefighters brought the blaze under control in the early hours of Monday, with smoke dissipating and initial air quality tests finding no toxic contaminants.
Authorities said the blaze, inside the GRI scrap yard on Underwood Street, was about 50 metres by 20 metres in size at its peak.
Eight units were called in about 5.30pm on Sunday to put out the fire, with support from Fire and Rescue NSW's Queanbeyan crews.
Six ACT Fire and Rescue crews were still at the scene on Monday and expected to extinguish the blaze by the afternoon.
Firefighters planned to remain at the scrap yard for most of the day as air quality testing continued.
An excavator was also being used to pull apart piles of vehicles and other materials as crews work to dampen down the burnt area and extinguish the fire.
The Country Rail Network said normal service had resumed on the line between Queanbeyan and Canberra after it was closed on Sunday night.
ACT Fire and Rescue chief officer Mark Brown said the initial firefighting efforts were "quite dramatic".
"We had exploding gas cylinders, and a high risk that that fire could actually leave the site and effect adjoining properties," Mr Brown said.
"Firefighters did a great job in the early stages and were able to confine that fire to the recycling facility."
Mr Brown said firefighters were investigating what caused the fire, but given the amount of material at the site, it would be very difficult to identify the point of origin.
A worker at the GRI scrap metal yard, who would not give his name, said he believed the fire had started outside the yard and spread inside.
"It appears, from CCTV, to have started outside the yard and spread into the yard at about 5.30 last night," he said on Monday morning.
"We haven't even talked to the police yet, or the fire brigade for that matter, so I don't want to go shooting my mouth off too much and I can't really tell you anything more."
Helen Anley, who lived about a five-minute walk from the scene of the fire, which was on an industrial estate in the suburb of Beard, said she heard several loud bangs.
"I was at home and I heard a big explosion," Ms Anley said.
"I thought maybe someone had lit a gas cannister on fire or something. And then I saw the massive plume of black smoke."
Queanbeyan resident Adam Keesing said he heard the explosions from his house nearby.
"I heard the bangs from my house and wondered what it was," he said.
"I only live three or four blocks away."
NSW Police closed off the Canberra Avenue exit leading to the industrial estate on Sunday night as the fire burned out of control.
Residents in Queanbeyan West, Jerrabomberra, Karabar and Harman were advised on Sunday night to stay indoors with doors and windows closed.
On Monday, the Emergency Services Agency said smoke was no longer having an impact on the surrounding area.
People with asthma or a lung condition should follow their personal asthma or Chronic Obstructive Pulmonary Disease plan.