CAMBRIDGE — Firefighters tackled a massive fire at a recycling plant on Conestoga Boulevard in Cambridge late into Monday evening.

The Waste Management building, touted as Ontario's largest private-sector facility on its website, filled up with smoke a little after 5:30 p.m.

It was promptly evacuated and no one was injured, said Fire Chief Neil Main.

Spokesperson for Waste Management, Luiza Adsett, said 25 employees were inside.

"We don't know the cause yet," Main said.

Main said the fire began in the back of the building where cardboard recyclables are sorted and compressed. He also said there were working sprinklers in the building.

"The flames are still going," he added. "The thick smoke means that is where the fire is."

The short street between Bishop Street and Sheldon Drive was closed to traffic. There was a shelter-in-place order for the surrounding area.

Large plumes of thick, black smoke permeated the air and were also visible along Hespeler Road.

Dozens of people watched from nearby parking lots as 20 firefighters doused the flames with heavy streams of water. Main said he had four stations on scene but needed to call on six more firefighters to assist.

Around 7 p.m., part of the roof collapsed but no one was injured.

The fire continued to burn into the late evening. Main said it could take several hours to completely extinguish.

At one point, firefighters took an axe to the plastic siding of the large building, trying to create holes for ventilation. Thin streams of black smoke seeped out.

Main did not have a damage estimate as firefighters continued to battle flames and thick smoke, but he did say there was "lots of damage."

"We do not have it under control yet."

The building was acquired by Waste Management in 2012. Cardboard, paper, glass, plastics, metals and other recyclables are sorted and processed.

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Adsett said the building will reopen when it is safe to do so. Until then recyclables will be redirected to other plants in the province.

- Damage estimate $15-million after fire guts Cambridge recycling centre