Investigators from Ontario’s Office of the Fire Marshal are on the scene after a massive blaze gutted a meat processing plant in Burlington, Ont., sending up an enormous cloud of smoke that blanketed the area and triggered several road closures.

Fire crews were called to the Paletta International Corporation building at 4 p.m. on Wednesday, near Highway 403. A total of 14 fire vehicles and more than 40 firefighters attended the scene to fight the blaze, which consumed approximately half of the industrial building.

All of the employees were able to get out of the building safely, CTV Toronto’s John Musselman reported. It’s not clear how many people worked at the plant or what will happen to their jobs in the coming days, he said. CTV Toronto has reached out to officials from Paletta International for more information but is still waiting to hear back.

The cause of the fire is not yet known.

Burlington Fire Chief David Lazenby said crews quickly moved to contain the fire rather than going in to put it out.

“We fight the fire from the outside,” he told CTV Toronto. “We did that both for the safety of the firefighter and the fact that all people, all staff employees had been accounted for.”

Fire officials say there was also some concern about entering the building because ammonia tanks were known to be on the premises.

“There are some tanks containing ammonia inside the building and as a precaution and with the smoke it was best to ensure people were safe,” Insp. Ivan L’Ortye from Halton Regional Police said.

Employees at neighbouring buildings in the industrial area were advised to stay inside due to the smoke. There was also some concern that it might blanket the nearby QEW highway during evening rush hour, but favourable winds prevented that from happening.

Witness Tim Dyson, who was leaving work at the time of the fire, said it broke out quickly. “It started getting heavier and heavier, and then we heard the sirens coming,” he said.

Firefighters remained on scene through the night.

Police say an inspector from the Ministry of the Environment has already investigated the scene. Air quality tests were conducted and no dangerous fumes were detected, Musselman said.

With files from CTV Toronto