( dpa ) - The gender and race factors in Saturday's Democratic primary in South Carolina were being closely watched as competition between Senators Hillary Clinton and Barack Obama intensified for their centre-left party's presidential nomination.
With economic worries soaring as the US stock market slumps and unemployment rises, the candidate seen as the strongest on the economy could also come out ahead, as did Clinton in the New Hampshire and Nevada primaries for similar reasons.
Polls opened at 1200 GMT on a sunny, 10-degree-Celsius day in the first Democratic contest in the US South and the first presidential primary not being played out before an overwhelmingly white electorate.
About half of the state's 2.5 million eligible voters are African- American. Many voted last week in the Republican primary, giving Senator John McCain, 71, top billing for Republican delegates to the national convention later this year.
A bitter contest divided Democratic voters in South Carolina between Clinton, 60, who is hoping to become the country's first woman president, and Obama, 46, who is bidding to become the first African-American in the White House.
It has even divided one famous civil rights family, with Jacqueline Jackson making a radio ad aired in the state for Clinton while her father, the Reverend Jesse Jackson, a South Carolina native and one-time presidential candidate, is backing Obama, the State newspaper in Columbia, South Carolina, reported.
Obama held a about a 10-percentage-point lead over Clinton in state polls through the week, but such figures can deceive. Going into the New Hampshire primary earlier this month, Obama led by double digits in opinion polls but lost the vote by 2 per cent to Clinton.
Former senator and 2004 vice-presidential nominee John Edwards, 54, a native South Carolinian, had moved up in the polls after a strong performance in a debate earlier this week but still trailed in third place.
To date, Obama has claimed one primary victory in Iowa, while Clinton has claimed New Hampshire and Nevada. All three wins were connected to strong support among women voters.
But with the large number of black voters in South Carolina, the race factor could decide the outcome, according to opinion polls. An MSNBC-McClatchy poll released Thursday showed 36 per cent of South Carolina Democratic women backing Obama, and 33 per cent for Clinton.
White women backed Clinton at 43 per cent with Edwards at 34 per cent and Obama at 8 per cent, the State newspaper reported. Black women favoured Obama with 55 per cent, Clinton with 27 per cent and Edwards with 4 per cent.
Clinton spent eight years as first lady in Arkansas, another Southern state, when Bill Clinton was governor. Her husband, who later rose to the White House, was popular with black voters and has drawn controversy in the South Carolina contest with strident verbal attacks on Obama.
Obama has placed "change" from conventional Washington politics at the heart of his campaign and portrayed himself as a candidate who can transcend the issue of race. He has strong generational appeal among younger voters.
In addition to having been born in the state, Edwards once served as US senator from neighbouring North Carolina and won South Carolina in his 2004 bid for the Democratic presidential nomination.
He has made ending poverty a lifetime goal that plays well in the poorer, Southern states, and even launched his candidacy last year from the impoverished New Orleans quarter that was among the worst- flooded by Hurricane Katrina.
National polls show Obama leading Clinton among black voters. Clinton leads among white voters, women and overall in the Democratic Party ahead of the crucial, so-called Super Tuesday on February 5, when more than 20 states will vote in primaries that could be enough to decide the nomination.
On Tuesday, centre-right Republicans will cast presidential preference ballots in Florida, where the fate of former New York mayor Rudy Giuliani's lagging campaign will likely be determined.
The candidates are competing for delegates to nominating conventions in August and September before the November 4 general elections.