Republican US presidential candidate Donald Trump on Sunday levelled an attack against Taylor Swift, declaring his "hate" for her just days after the pop mega-star endorsed his Democratic opponent, Kamala Harris.

In an all-caps posting on his Truth Social media account, Trump wrote: "I HATE TAYLOR SWIFT!"

Immediately following last week's Trump-Harris debate, Swift informed her 284 million Instagram followers that she planned to vote for Harris, currently the US vice president, "because she fights for the rights and causes I believe need a warrior to champion them."

Trump initially dismissed Swift's endorsement of Harris by simply saying he was "not a Taylor fan."

But since then, with public opinion polls showing Harris gaining significant ground on Trump in what is expected to be a close November 5 presidential election, the former president has ratcheted up his rhetoric against one of the most successful recording artists in history.

Swift's backing of Harris has drawn over 9 million "likes" to her Instagram post, fuelling speculation that it could boost the Democrat's chances of winning the presidential election. (Reuters)