Retired neurosurgeon Ben Carson has said he will run for US president, joining an already overflowing field for the Republican nomination as the party's first black candidate for 2016.

"I'm willing to be part of the equation and, therefore, I'm announcing my candidacy for president of the United States of America," Carson told a local CBS station in West Palm Beach, Florida.

Carson, 63, is a political novice with decades of fame because of his career as a pediatric neurosurgeon at Baltimore-based Johns Hopkins Hospital. In 1987, Carson performed the first successful separation of conjoined twins.