Leading Republican presidential candidates Newt Gingrich and Mitt Romney sparred over immigration policies as the latest surveys showed the two locked in a tight race before Tuesday's primary in Florida.

Bouncing off his South Carolina primary victory, former House speaker Gingrich has surged to match former Massachusetts governor Romney in polls in Florida, a state in which 50 delegates are at stake in the winner-takes-all contest.

Romney once led Gingrich by double-digit margins in Florida, and his campaign and its allies have been blanketing the airwaves in recent days with ads that are highly critical of Gingrich.

A CNN/Opinion Research Centre poll released Wednesday found Romney leading Gingrich by two points, 36 to 34 percent, among likely voters. That's within the polls margin of error.

The other two candidates are far behind, with Rick Santorum at 11 percent and Paul at 9 percent, with 7 percent unsure of who they'll vote for.

A Quinnipiac University poll released Wednesday also found likely voters favouring Romney over Gingrich, 36 percent to 34 percent.

Public Policy Polling found Gingrich further ahead among likely primary voters - with 38 percent support - and Romney in second place with 33 percent. That poll, released Monday, represented a 12 point gain for Gingrich, and an 8 point drop for Romney in just one week.

Only one survey - done by the American Research Group - found Romney leading Gingrich by a wider margin of seven points. The survey of likely Republican primary voters showed Romney with 41 percent and Gingrich with 34 percent.

The candidates have also been trying to win the Hispanic vote, which could make the difference in a tight race. The one million Cuban-Americans concentrated in South Florida tend to vote Republican.

According to an ABC News/Univision survey released Wednesday, Romney has a 15 point lead over Gingrich among Hispanic voters. Romney took 35 percent of respondents' support compared to 20 percent for Gingrich, while 20 percent of Hispanic voters remained undecided.

During Thursday's debate, Gingrich charged Romney' with being the most anti-immigrant candidate whose immigration policy would result in the deportation of grandmothers who are in the country illegally.

Romney, who has advocated for "self-deportation", a policy that involves making economic conditions so difficult for undocumented workers that they choose to leave the country to find better opportunities in turn accused Gingrich of using "highly-charged epithets" irresponsibly.