MIAMI — White House hopeful Mitt Romney has opened up a commanding double-digit lead in Florida against main rival Newt Gingrich in their Republican nomination battle, the latest two polls showed on Sunday.

Romney, a former Massachusetts governor and millionaire venture capitalist who is considered the party establishment's favored candidate, was routing former House speaker Gingrich by 15 points, 42 percent to 27 percent, just two days before the crucial Florida primary, according to an NBC/Marist poll.

The Miami Herald in its own poll published Sunday shows Romney ahead by 11 points.

Both surveys showed Christian conservative former senator Rick Santorum a distant third and libertarian-leaning congressman Ron Paul fourth.

Gingrich insisted on Fox News Sunday that the race for the large southeastern state would be "close," but the poll figures showed otherwise.

"What does Gingrich need to do? I would say Romney would need to implode," Brad Coker, the pollster who conducted the Miami Herald survey of 800 registered Florida voters, said in the newspaper.

"If there's no 11th-hour surprise... this race is looking right now like it's over."

Lee Miringoff, director of the Marist Institute for Public Opinion at Marist College, which conducted the NBC poll, also said Romney appeared headed for a decisive Florida victory.

"The bottom line in all this is Romney's sitting in the driver's seat going into Tuesday," Miringoff said on the MSNBC website.

Florida is the most populous swing state in the country and promises to be the scene of a major campaign showdown ahead of November's general election in which Republicans will seek to oust President Barack Obama, a Democrat.

The two polls were split on whether Obama or Romney would win in a November matchup.

NBC has Obama trouncing all Republicans, including Romney by 49-41 percent and Gingrich by a whopping 52-35 percent. But the Herald poll showed Romney beating Obama 48-44 in a theoretical general-election matchup, whereas Obama was seen winning handily in a face-off against Gingrich.

Both surveys have a margin of error of about 3.5 percentage points.