President Donald Trump said Thursday that conservative economic commentator Stephen Moore has withdrawn from consideration to become a member of the Federal Reserve Board, the president's second candidate to pull out.

"Steve Moore, a great pro-growth economist and a truly fine person, has decided to withdraw from the Fed process," Trump said on Twitter, moments after Moore told Bloomberg and The Wall Street Journal that he would stay in the race.

Trump's other candidate, businessman and long-shot presidential candidate Herman Cain, also pulled out of the race to fill one of two remaining openings on the central bank board.

Trump has repeatedly ignored norms designed to protect the independent Fed from political influence, which could undermine its credibility, lambasting the central bank for raising interest rates and even this week calling for a drastic cut.

In that atmosphere, his nominations of Moore and Cain were viewed by some as an attempt to bring pressure from the inside. They also were criticised for their lack of qualifications, including by Republicans in the Senate.

Five of the 53 Republicans in the 100-member chamber told AFP there were serious problems with Moore's candidacy, adding to concerns that at least two other Republican senators had shared with reporters in recent days.

Senator Joni Ernst of Iowa hardened her opposition after the emergence of articles and speeches by Moore over the years, some of which have been criticised as sexist or trafficking in racism.

Moore, a 59-year-old economic and political commentator, advised Trump when he was running for president and has publicly expressed his opposition to raising interest rates.

He gave two interviews published within an hour of Trump's tweet saying he was staying in the race, and that a White House official had encouraged him to remain.

"I sure am," Moore told Bloomberg when asked if he would persist in seeking a Fed seat. "I'm not too concerned about this."

Trump said on Twitter that he asked Moore "to work with me toward future economic growth in our Country."

The Fed has a seven-member board, but has had openings for many months.

Trump has named three current Fed members to the board, including Vice Chairman Richard Clarida, and also promoted Jerome Powell to his current post as board chair.