Three construction workers were seriously injured at job site in Brooklyn, fire officials said.

The men were working on a building on 21st Street near the Gowanus Expressway when the were struck by a steel plate that came loose around 9 a.m., according to the FDNY.

Two were taken Lutheran Hospital and one was taken to Methodist Hospital. All three were said to be in serious condition.

It was not immediately clear what caused the accident, officials said.