|Former governor Romney attacked Gingrich this week over his ties to the mortgage agency Freddie Mac [Reuters]
Voters in Florida are going to the polls in the latest primary contest for the Republican nomination to take on Barack Obama in November's presidential election, with Newt Gingrich struggling to halt surging rival Mitt Romney's momentum.
Polls opened in the southern state at 7am local time (1200GMT) on Tuesday, with Romney, the former governor of Massachusetts, holding a double-digit lead over his main rival, according to most surveys.
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But Gingrich, the former House speaker who won the last contest in South Carolina, said the race was closer in Florida than the polls indicated and vowed to fight on beyond Tuesday's vote.
Conservatives eventually would rally behind his candidacy and block Romney's nomination, he said.
"I believe the Republican Party will not nominate a pro-abortion, pro-gun control, pro-tax increase moderate from Massachusetts," Gingrich said after attending a Baptist church in Lutz, Florida.
"They will not nominate somebody who raises millions from Wall Street to run ads that are false. So this is going to be a straight out contest for the next four or five months."
Earlier, Gingrich accused Romney of distorting his record. "He has a basic policy of carpet-bombing his opponent," he told Fox News.
"I give Governor Romney's campaign due respect for the sheer volume of negativity that they use and the sheer amount of money they raise on Wall Street."
'Winner takes all'
Rick Santorum, a former Pennsylvania senator, and Ron Paul, a US congressman from Texas, are also still in the race to challenge Obama.
Al Jazeera's Alan Fisher, reporting from Tampa, said the Florida primary was a "winner takes all election".
"All the delegates are up for grabs here. There are 50 delegates going to the convention, and the winner takes all here. Coming in second means absolutely nothing. That is why the candidates are badmouthing each other so much."
Romney told supporters in Naples, Florida, that Gingrich was making excuses and should take a look in the mirror.
"My own view is that the reason Speaker Gingrich has been having a hard time in Florida is the people of Florida have watched the debates and listened to the speaker, have listened to the other candidates, and have said, 'You know what? Mitt Romney's the guy we're gonna support'," he said.
Romney this week attacked Gingrich for his ties to the mortgage agency Freddie Mac and the collapse of the housing market - an open wound in Florida, where residential property values have plunged about 45 per cent since early 2006.
Gingrich picked up the endorsement on Saturday night of former rival Herman Cain, who dropped out of the Republican race in December after allegations of sexual harassment and an extramarital affair.
But polls have shown the race moving toward Romney in Florida for days, reversing the momentum that Gingrich built after scoring an upset by defeating Romney in South Carolina on January 21.
A Reuters/Ipsos poll showed Romney, the former Massachusetts governor, holding a 12 percentage point advantage over Gingrich in Florida. Three other polls on Sunday put Romney's lead in Florida at between 11 and 15 points.
"It's clear that Romney has run a much more focused and effective campaign in Florida than Newt," Republican strategist Matt Mackowiak said. "Newt is playing defence every single day in every way."