SAN ANTONIO: A federal judge in San Antonio finds himself at the centre of an uproar after telling newly sworn US citizens that Donald Trump is "your president, and if you don't like that, you need to go to another country."

US Magistrate Judge John Primono's comments were reported by KENS-TV in San Antonio, which covered the naturalisation ceremony at which 500 immigrants took the oath of US citizenship at the Institutes of Texan Cultures on Thursday.

"I can assure you that whether you voted for him or you did not vote for him," the television report quoted him as saying of the president-elect, "if you are a citizen of the United States, he is your president. He will be your president, and if you do not like that, you need to go to another country."

He later told the station and the San Antonio Express-News that he meant his words to be unifying and respectful of the president's office, not political, and added that he did not vote for Trump for president.

"I wasn't trying to say anything for or against Donald Trump. I was just trying to say something hopeful and unifying, and unfortunately it was taken out of context," he told the Express-News.

The television station also reported that Primono was critical at the ceremony of protesters who carried placards saying, "He's not my president," and said he detested the actions of pro athletes who kneel during the playing of the national anthem.

Primono, the son of German and Italian immigrants, has been a magistrate judge since 1988.