The 11-alarm fire broke out around 8:15 p.m. Friday at the Majestic Industries warehouse on Passaic Street.
Saturday morning, after working through the night in freezing temperatures, fire crews were still working to douse the flames.
As of 7 a.m., the fire was not completely under control, but was contained, Mayor Hector Lora said.
The fire started in the Majestic industries warehouse, where the company manufactures gaming and hospitality furniture for casinos and bingo halls and spread to an adjoining building used by Qualco Inc. to produce chlorine pellets used to treat pools and spas.
No one was in the complex when the fire started except for the security guard who called authorities.
"So I immediately run to the office, get authorities on the phone, the fire department and try to do the best I can try to save the building. But you know, it's dangerous," security guard Justin Johnson said.
Johnson said he thinks the fire began in the stackhouse area near the roof.
"I open the gate, I see fire from the roof and by the stackhouse area," he said. "It was a blessing I got out of there. I treat that building like it's my own. I work there, it grows onto you. It hurts a little bit."
Together the two buildings spread over more than 200,000 square feet and Lora said the fire had the potential to be the worst the city had ever seen.
Officials were concerned about possible air quality issues, however, firefighters' quick work kept the flames from reaching the area where more than 100,000 pounds of chlorine pellets are stored.
There was further concern about possible evacuations from a nearby residential area, but that was also avoided.
Gov. Phil Murphy made resources from the New Jersey Department of Environmental Protection agency available to assess the air quality.
"They made an assessment in terms of the air quality, as you can see behind us they continue battling this fire. But as a direct result of the remarkable response of firefighters and emergency responders they were able to contain the fire and it did not reach the main chemical plant," Lora said in a video posted on Facebook.
The air quality has been deemed safe and no mandatory evacuations were ordered.
Over a dozen firefighters were injured in trips and falls, including sprained ankles, bumps, and bruises, as the millions of gallons of water used to put out the flames froze almost immediately amid below freezing temperatures.
One firefighter was hit in the face by debris and taken to the hospital, but has since been released.
It's still too early to tell what causes the fire.
Officials say an investigation will begin once authorities are able to get inside the building.
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