Fresh off a runaway win in the South Carolina primary, Democrat Hillary Clinton turned her sights to a possible match up with Republican front runner Donald Trump in the 8 November presidential election.

Without mentioning the billionaire businessman’s name, the former secretary of state made it clear she was already thinking about taking on the real estate mogul whose recent string of victories made him the favorite to be the Republican nominee for the White House race.

Ms Clinton shot down Mr Trump's campaign slogan of "Make America Great Again" and his plans to build a wall on the US-Mexican border.

"Despite what you hear, we don't need to make America great again.

"America has never stopped being great," she told supporters in her victory speech in South Carolina, pausing for applause then adding, "but we do need to make America whole again."

"Instead of building walls, we need to be tearing down barriers," said Ms Clinton, who would be America's first woman president.

Ms Clinton said she was not taking anything for granted after crushing Democratic rival Bernie Sanders by 48 points and likely setting herself up for a good "Super Tuesday" night on 1 March, a key date in the nomination battle.

But if Ms Clinton and Mr Trump win big on Tuesday as polls suggest, the chance of a general election match-up between them increases, adding another twist to a presidential campaign that has defied convention as US voters vent frustration over economic uncertainty, illegal immigration and national security threats.

A Trump-Clinton election would embody the outsider vs establishment battle in American politics.

Mr Trump has never been elected to public office, while the former first lady has been a player in Washington for decades.

South Carolina was the third Clinton campaign victory in the first four Democratic contests, raising more questions about whether democratic socialist Bernie Sanders will be able to expand his support beyond his base of predominantly white liberals.

Exit polls showed Ms Clinton winning big in the state with almost every constituency.

She won nine of every 10 black voters, as well as women, men, urban, suburban, rural, very liberal and conservative voters. Mr Sanders was ahead among voters between ages 18 and 29, and among white men.

When asked which candidate they thought "can win in November," an overwhelming 79%  said Clinton, with only 21% putting their faith in Mr Sanders to defeat the eventual Republican nominee.

In the Republican race, Donald Trump and rival Marco Rubio accelerated their political slugfest yesterday during dueling appearances in Arkansas and Georgia.

"The majority of Republican voters do not want Donald Trump to be our nominee, and...they are going to support whoever is left standing that is fighting against him to ensure that we do not nominate a con artist," Mr Rubio told reporters in Georgia.

Ex reality TV star Mr Trump, speaking in front of his private plane in Arkansas, belittled his main rival and accused the first-term US senator from Florida of being fresh.

"I watched this lightweight Rubio, total lightweight, little mouth on him, 'bing, bing,  bing' ... and his new attack is he calls me a con artist," Mr Trump said.

 "The last thing I am is a con man."