A major fire is engulfing the site of what was once one of America's largest steel producers

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A major fire engulfed several buildings at the former Bethlehem Steel plant Wednesday morning.

A major fire is ripping through three connected buildings at the site of the former Bethlehem Steel plant - once one of America's largest steel producers.

More than 100 firefighters have been called to the site, which is the size of approximately six city blocks, the Buffalo News reported.

The fire reportedly broke out around 7 a.m., and was still not "under control" as of 10:15, Buffalo Fire Commissioner Garnell Whitfield told media. The site is located in Lackawanna, New York, just south of Buffalo.

The building ignited after a light bulb fell onto some combustibles, one Lackawanna official said.

Employees who work at the site, which is now home to several businesses, reported hearing a number of explosions from inside the building before the roof collapsed, according to the Buffalo News.

Whitfield said much of the building has already collapsed, and several types of materials are burning inside.

Photos posted on social media showed a massive plume of black smoke rising from the site and a heavy presence emergency response.