ST. LOUIS, Missouri (CNN) -- Polls in five crucial battleground states in the race for the White House released Wednesday suggest that Sen. Barack Obama is making some major gains.

Sen. Barack Obama has gained ground in key toss-up states, polls show.

The CNN/Time Magazine/Opinion Research Corp. polls of likely voters in Florida, Minnesota, Missouri, Nevada and Virginia suggest a shift toward the Democratic presidential nominee.

In Florida, the state that decided the 2000 presidential election, 51 percent of likely voters say Obama, D-Illinois, is their choice for president, with 47 percent backing Republican presidential nominee John McCain.

The last CNN poll taken in Florida two weeks ago showed the race for the state's 27 electoral votes tied at 48 percent apiece among registered voters.

A new CNN poll of polls in Florida, also out Wednesday, has Obama leading McCain by 5 points. The CNN poll of polls is an average of the new CNN poll and other new state polls.

"The campaign season is like the hurricane season," said Bill Schneider, CNN's senior political analyst. "Florida lies directly in its path. Hurricane Obama hit Florida, and Hurricane McCain. Tropical Storms Biden and Palin made landfall in the Sunshine State. The impact? Over the last two weeks, Barack Obama has been gaining support in Florida." Watch Bill Schneider's report on shifts in key battleground states. »

Obama's also making gains over McCain in Minnesota, the state in which the Republican convention was held a month ago. Fifty-four percent of those questioned are backing Obama, with 43 percent supporting McCain, R-Arizona. That 11-point lead is much larger than the 2-point advantage Obama had in the last CNN poll taken in Minnesota a month ago.

It's a similar story in Missouri, where 49 percent of those polled are backing Obama and 48 percent supporting McCain. That's a gain for Obama, who was down 5 points to McCain in CNN's last poll in Missouri, taken three weeks ago. The only other new poll in Missouri, a Research 2000 survey, indicates McCain ahead by 1 point.

Thursday's vice presidential debate will be in St. Louis, Missouri.

The poll also indicates Obama has a 4-point lead over McCain in Nevada, 51- 47 percent. CNN's last survey in Nevada, taken in late August, had McCain up slightly. A new American Research Group poll in Nevada puts McCain ahead by 2 points.

In Virginia, which hasn't voted for the Democrats in a presidential contest since 1964, the new poll suggests Obama has a 9-point lead, 53-44 percent.

The last CNN survey in Virginia, taken in mid-September, had McCain up by 4 points. But it's a slightly different story in American Research Group's new survey in Virginia, which indicates McCain has a 3-point lead. Watch 'The Situation Room' break down the numbers »

What's behind this shift for Obama?

"Obama has gained ground among moderates in all five states," said CNN polling director Keating Holland. "That may have something to do with the first presidential debate. Some commentators knocked Obama for agreeing with McCain as often as he did, but moderates tend to like it when candidates appear willing to see the other side's point of view."

"In most states, Obama also won support from senior citizens and voters making more than $75,000. Those are two groups who may have been hardest hit by the recent problems in the stock market and the financial community," Holland added. "Economic jitters may not last if Congress passes legislation in the next few days, but there may have been short-term gains for Obama as a result of the current economic problems." See bailout tracker »

The new CNN/Time Magazine/Opinion Research Corp. polls are behind a shift in the CNN Electoral College Map. CNN is moving Minnesota and its 10 electoral votes, from toss-up to leaning toward Obama. And Missouri, with 11 electoral votes, is shifting from leaning toward McCain to toss-up.

With those moves, CNN estimates that if the presidential election were held today, Obama would win states with 250 electoral votes and McCain would win states with 189 electoral votes, with 99 electoral votes still up for grabs. To win the White House, 270 electoral votes are needed. Obama's lead is up from 40 points in CNN's last electoral map updated last week.

The poll also expanded to include three third-party candidates: independent candidate Ralph Nader, Libertarian candidate Bob Barr and Green Party candidate Cynthia McKinney. Except for a 3-percent showing by Nader in Florida and a 4-percent showing by Nader in Nevada, no one registered more than 2 percent in any survey.

The CNN/Time Magazine/Opinion Research Corp. polls were conducted September 28-30, with 940 registered voters and 770 likely votes in Florida; 929 registered voters and 849 likely voters in Minnesota; 951 registered voters and 744 likely voters in Missouri; 924 registered voters and 684 likely voters in Nevada; and 925 registered voters and 684 likely voters in Virginia, all questioned by telephone.

The survey's sampling error is plus or minus 3.5 percentage points in Florida, Minnesota and Missouri, and 4 percentage points in Nevada and Virginia.

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