An amateur blacksmith started a fire that engulfed three blocks after attempting to imitate a sword-forging scene he had seen on TV, reports say.
John Gomes from the town of Cohoes in New York state was trying to bend metal in imitation of the TV series Forged in Fire when the yard blaze started.
The series shows professional bladesmiths competing to make “history’s most iconic edged weapons”.
It was the “worst disaster the city has ever seen,” Mayor Shawn Morse said.
Fanned by high winds, the flames destroyed three buildings and damaged 18 others. It was brought under control after three hours but then started up again an hour later, CBS reported.
Twenty people were displaced and a firefighter was taken to hospital with unspecified injuries but no-one else was hurt, the Albany Times Union reported.
Mr Gomes, 52, has been charged with reckless endangerment and arson and is in custody, the newspaper said.
“We often tell people we don’t allow open burns in the city and they often say, ‘What’s the worst that could happen? Well, this open burn just caused millions of dollars of damage and destroyed half our downtown,” CBS quoted Mr Morse as saying.
Mr Gomes’s teenage son defended his father on Facebook.
“My father John Gomes didn’t mean to burn his house down,” 16-year-old John Gomes wrote, the Albany Times Union reported.
Assistant police chief Tom Ross said the fire had been started unintentionally.