WASHINGTON (AFP) - United States Vice President Joe Biden is taking Republican presidential frontrunner Donald Trump to task over his "sick" comments on immigration.

Addressing a group of Hispanic Americans, Biden - who is currently weighing a run at the presidency in 2016 - lashed out Tuesday at the real estate mogul who has described Mexican immigrants as rapists.

"I walked out of the house just as Trump was talking on the television," Biden told the gathering. "Folks, this will not prevail. This will not prevail."

"That one guy absolutely denigrated an entire group of people, appealing to the baser side of human nature, working on this notion of xenophobia in a way that hasn't occurred in a long time. Since the 'Know Nothing' party at the end of the 19th century." Hispanic Americans make up a large and growing section of the US electorate.

Many in the Republican camp fear Trump's populist message will hurt the party with minority voters, an area where it is already weak.

Democrats have been keen to capitalise on the issue, but Biden said it was not about Democrat or Republican, "it's about a sick message." "This message has been tried on America many times before. We always, always, always, always, always overcome," he said.

"Folks, the American people are with us," he said. "I know it doesn't feel that way. But I'm telling you. I'm telling you. The American people agree with us." Heading into the second Republican debate Wednesday, Trump has a substantial lead in the polls.

He is well ahead in the three key states that kick off the nomination race, Iowa, Florida and South Carolina, in some cases by double digits.

His durability has surprised pundits, but has electrified the Republican base, which is infuriated at seven years of Democratic rule and angry at the party establishment.