US Republican presidential candidate Donald Trump has apologised for lewd comments he made 11 years ago referring to women's body parts and his attempts to get women to sleep with him.

Trump made the comments apparently unaware he was being recorded while on his way to a television taping with a celebrity gossip television show in 2005.

He issued the apology after The Washington Post revealed the video of Trump caught on a hot mic while talking with Billy Bush of Access Hollywood.

The recording begins with Trump bragging he had "moved" on a married woman "very heavily," and then saying he was rebuffed.

Trump is heard saying he "did try and f--- her,'' referring to an unknown woman. He also used graphic terms to describe the woman's body.

After Trump and Bush notice Arianne Zucker, an actress on Days of Our Lives, Bush makes a comment about her being "hot as s---".

Trump says, "I've gotta use some Tic Tacs, just in case I start kissing her. You know I'm automatically attracted to beautiful - I just start kissing them. It's like a magnet. Just kiss. I don't even wait."

"And when you're a star they let you do it. You can do anything."

"Whatever you want," someone else, possibly Bush, says.

In his apology Trump referred to the statements as "locker room banter".

The conversation was private and took place many years ago, he added.

"Bill Clinton has said far worse to me on the golf course - not even close," he said. "I apologise if anyone was offended."

Democratic presidential candidate Hillary Clinton said on Twitter, "This is horrific. We cannot allow this man to become president."