America's first couple have gone on the offensive against Donald Trump , denouncing the Republican's reported sexual aggression toward women.

Tapes that have surfaced over the past week of Trump's lewd comments about women have "shaken me to my core", said First Lady Michelle Obama as she campaigned for Hillary Clinton in New Hampshire, last night (13 October).

An out-take from a 2005 Access Hollywood segment released a week ago captures Trump saying that it was all right for powerful men like him to grab women by the genitals. "I'm automatically attracted to beautiful women, I just start kissing them. I don't even wait," he said. "And when you're a star they let you do it."

Obama said this was not "just a lewd conversation" or "locker room banter" but exposed a "powerful individual speaking freely and openly about sexually predatory behaviour". She called the belief that someone could do anything they want to a woman "cruel" and "frightening".

Several women have spoken out since the video appeared with allegations of Trump's indecent behaviour toward them stretching back decades.

"I am going to be dating her in 10 years. Can you believe it?" Trump was heard saying to a group of underage girls in another out-take — this time from a 1992 Entertainment Tonight segment filmed at Trump Tower — that turned up midweek.

In a separate campaign stop for Clinton in Columbus, Ohio, President Barak Obama said that the Republican Party leadership was to blame.

"The people who knew better didn't say anything," Obama said. "They didn't say... we can't allow our politics to descend into the gutter. They stood by while this happened."