About 10 companies and 175 firefighters responded to the blaze, which was the equivalent of four alarms, Wood said.
As they battled the towering flames, the mansion was veiled in white smoke that would occasionally clear enough to reveal the charred remains.
"It's a shame. They just don't make them like this anymore," said Jeff Bader, a nearby resident.
The estate was originally the site of the Victorian home of Albert Eugene Gallatin, which was built around 1885.
George McFadden Jr., a cotton tycoon, acquired the estate, and in the early 1920s he hired famed Philadelphia architect Horace Trumbauer to remake the main residence in the style of a chateau, according to the Radnor Historical Society.
It became known as Bloomfield, the name of a branch of the family, the historical society reported in a 1988 newsletter article.
McFadden died when he was electrocuted by a steam cabinet in a bathroom, the article said, but the estate remained in the family until 1984.
In late 2010, the 5.87-acre estate served as a double for Gracie Mansion, the official residence of New York City's mayor, for the Jason Statham action movie Safe, which is scheduled to open in theaters April 27.
Bloomfield, listed for sale last year at $6.9 million, had 19 bedrooms and nine full baths in its 22,000-plus square feet of living space, officials said.
County records show the property is owned by Jerald Batoff, the son of the late William Batoff, a prominent Democratic fund-raiser.
Contact Bonnie L. Cook at email@example.com.