Former US ambassador to the United Nations Nikki Haley has denied speculation that she would serve as Donald Trump's vice president if he wins the Republican nomination.

Haley was speaking to voters at a campaign stop in New Hampshire, the second battleground in the Republican primary to select a candidate for November's US Presidential race.

US media reported that Haley said she does not want to be anybody's vice president and added that's off the table. She made the remarks in a local diner.

Recent polls show Haley going after Trump, who won the Iowa caucuses, the Republican's first nomination contest, by a large margin. Both are campaigning in New Hampshire ahead of Tuesday's primary.

On Friday, Trump invited Republican Senator Tim Scott from South Carolina to a campaign rally in the state. Haley is a former governor of the southern state. Scott, too, had sought the party nomination but ended his campaign last November. He endorsed Trump at the rally.

All eyes are on the New Hampshire primary, one of the early highlights of the Republican nomination race.