A massive fire at a Dietz & Watson warehouse in Delanco, Burlington County, blazed for a second day Monday.

Fire officials aren't sure what caused the fire, but by midday it was pretty much under control.

Still, columns of black smoke billowed from the massive distribution center Monday afternoon, with flames visible from within the severely damaged facility.

"We're going to probably have this for a day or two," Delanco deputy fire chief Bob Hubler told reporters. "We're doing our best to get into it from the exterior, but we're having a hard time reaching the center of the fire. That's been our problem the whole time: the center of this building has been burning."

Officials say they're monitoring the air and the black smoke is not toxic. At midday, officials said much of the smoke was caused by burning butter.

With both roof and wall collapses, Dietz & Watson CEO Louis Eni says the damage is extensive. But he was thankful it was an off day when the fire burst out.

"The most important thing is that there was no injuries whatsoever," Eni said. "The second-most important thing is that we service our customers — and that's what we're going to do."

Fire officials did report two very minor injuries to firefighters. Though the cause of the fire is currently under investigation, officials did say it appeared to start on the roof.

Rooftop solar panels were said to complicate efforts to fight the blaze.