Fists have been flying at the Bronx juvenile-detention center where Rikers teens were transferred — and apparently, so has the furniture.

A teacher at the Horizon Juvenile Center said he and other instructors begged city officials to bolt down chairs and other easy-to-throw objects when the 16-year-old defendants were moved in as part of a criminal-justice-reform program.

“Furniture has been flying, almost on a daily basis,’’ he said. “I’ve seen with my own eyes a thick security window that has been broken during the riot [The Post] covered, by a student hitting it with a classroom chair.

“Kids can’t learn when they don’t feel safe,” the anonymous teacher said of Wednesday’s brawl.

City education and correction officials met with reps from the United Federation of Teachers on Friday and agreed to bring over secure furniture from Rikers Island.