Atlanta, Georgia - Kamala Harris on Sunday said her election rival Donald Trump "demeans" the office of the president with his language, a day after the Republican called her "a s*** vice president."

Speaking in an interview with Reverend Al Sharpton on MSNBC, Harris said Trump's comment was an insult to the office and degraded the country's moral authority internationally.

"What you see in my opponent, a former president of the United States, really it demeans the office," she said, in response to a question about the comments.

"Donald Trump should never again stand behind the seal of the president of the United States. He has not earned the right."

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Harris said her opponent undermined the US' supposed "self-appointed authority" to speak on issues such as democracy and the rule of law.

With just over two weeks to go until Election Day, polls show Harris and Trump are locked in a neck-and-neck race for the presidency, including in the key swing states that decide US elections.

Trump has increasingly gone off-script during campaign events, using violent and sometimes bizarre language.

At the event in Pennsylvania during which he insulted Harris, the 78-year-old went off on a 15-minute tangent about golf legend Arnold Palmer and the size of his genitals.