The major fire broke out at the ACT government's Materials Recovery Facility, at the intersection of John Cory Road and Recycling Road late Monday night and extensively damaged both the structure and the heavy plant equipment.

The fire is expected to smoulder and potentially reignite for days as material is dragged out using heavy equipment and systematically hosed down.

After receiving a comprehensive briefing from the Emergency Services Agency and City Services on Tuesday, City Services Minister Chris Steel Minister said it appeared the Hume facility, together with its "discovery hub" education centre, was a totally write-off.

"The destruction of this facility is a significant setback for recycling in the ACT but also for six councils in NSW which send their material here to be processed," he said.

At this stage, Canberrans are still being told to put out their yellow recycling bins as normal.

But where that comingled recyclable material ends up in the medium term is the major unanswered question given the ACT processing facility was the largest operated within NSW and the ACT by the contractor Re.group.

"We will be temporarily storing that [comingled recyclable] material at Mugga Lane Resource Management Centre while we put in alternative arrangements to process and transport that material," he said.

The most likely outcome involves double-handling all the non-processed recyclables by placing them in container trucks and sending it north up the Federal Highway - provided a facility that will accept them can be found in Sydney.

The irony in this is that a major portion of Sydney's putrescible waste is compressed in containers and sent south by rail to be dumped in a former mine at Tarago, near Goulburn, by one of Re.group's waste management competitors, the French multi-national company Veolia.

"We will be working closely with Re.group as to what options are available to take this material over the coming days and weeks," Mr Steel said.

The cause of the multi-million dollar fire is still be determined and may not be known for some days.

Highly condensed recyclables like plastic, glass and cardboard inside the warehouse have been fueling the flames.

The toxic smoke from the smouldering fire is likely to rise and fall in volume as the material is progressively hosed down.

"Smoke is likely to be visible across the south Canberra region, including Jerrabomberra, Queanbeyan, Tralee, and surrounding NSW communities. If affected, close windows and remain indoors," the agency said.

Glues and resin in the cardboard are reigniting, causing the extra time to fully extinguish the fire.

Authorities plan to bring in heavy machinery from the nearby Mugga tip to move the materials out of the centre, to allow it to be properly put out and stop it reigniting.

There is about 150 tonnes of loose, unprocessed, fire-affected material sitting in the facility.

It will be brought out using machinery, broken open and spread out. It will be placed under a large hose and a special class A foam, containing a wetting agent, will be used to soak it down.

It is expected that this burnt material will need to end up in landfill.

Firefighters do not know how the fire started, but are investigating whether it was caused by lithium-ion - Li-ion - batteries. These have previously started fires in recycling centres.

The ACT's Chief Fire Officer, Matt Mavity, said his investigative team will examine the possible cause once the fire is completely out.

"Any battery storage, it doesn't matter what the chemistry is, has energy stored within it and can be released if damaged," he said.

"We're also informed by the operators [of the Hume facility] that products from vaping have latent heat in them so we're not ruling that out at this stage either."

The first triple zero call came in at 10.42pm on Monday. When the first of the firefighting crews arrived, they found fire both outside and inside the building at the rear.

They began fighting the fire inside the building but as it quickly spread, the fire crews switched from an offensive strategy to a defensive one. By this stage, witnesses say the fire was generating thick, roiling black clouds of smoke and intense heat was melting the downpipe, buckling the steelwork and shattering the skylights.

It took some six hours for firefighters to bring the fire fully under control because of the toxins contained within the smoke and the potential for the structure to collapse under the heat.

The building, which covers an area of 100 metres by 30 metres, was fully engulfed, but the fire did not spread beyond that.

Multiple CCTV cameras are fixed in high locations around the building and investigators are hoping to recover that hard-drive footage.

A staff member for Re.group, the contractor that manages the facility, reported the fire after spotting it on CCTV.

At its peak, 18 ACT Fire and Rescue trucks were at the scene, supported by paramedics and police.

The ACT government had announced in August this year that, together with funding from the Commonwealth, it planned to build a more modern processing facility next door. This was expected to cost around $23 million.

"That [new facility] wasn't planned to be operational until the end of 2024," Mr Steel said.

"We will be looking now to doing what we can to expedite that facility so that we can bring it online earlier so that we don't have to transport our waste interstate."

After the cardboard, plastics and steel were sorted and processed at the Hume Materials Recovery Facility, these materials were then collated, condensed, bundled and sent interstate for "remanufacturing".

The Hume facility was one of the largest in Australia, processing around 60,000 tonnes per year of commingled recycling received from the ACT and local NSW councils.

John Cory Road, Hume, is closed as of late Tuesday morning, but the Monaro Highway and Mugga Lane are open.

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