Hillary Clinton secured the Democratic Party's U.S. presidential nomination on Tuesday, coming back from a stinging 2008 defeat in her first White House run and surviving a bitter primary fight to become the first woman to head the ticket of a major party in U.S. history.

In a symbolic show of party unity, Clinton's former rival, U.S. Senator Bernie Sanders of Vermont, told the chairwoman from the convention floor that Clinton should be selected as the party's nominee at the dramatic climax of a state-by-state roll call at the Democratic convention in Philadelphia.

"I move that Hillary Clinton be selected as the nominee of the Democratic Party for president of the United States," Sanders told thousands of delegates in the Wells Fargo Centre, which erupted in cheers.

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Capping nearly a quarter century in public life as first lady, U.S. senator and secretary of state, Clinton will become the party's standard-bearer against Republican nominee Donald Trump in the Nov. 8 election when she accepts the nomination on Thursday.

In nominating Clinton, delegate after delegate made the point that the selection of a woman was a milestone in America's 240-year-old history. U.S. women got the right to vote in 1920 after ratification of the 19th Amendment to the Constitution.

Clinton, who promises to tackle income inequality and rein in Wall Street if she becomes president, is eager to portray Trump, a businessman and former reality TV show host, as too unstable to sit in the Oval Office.

But Trump, who has never held elective office, got a boost in opinion polls from his nomination at the Republican convention last week. He had a 2-point lead over Clinton in a Reuters/Ipsos opinion poll released on Tuesday, the first time he has been ahead since early May.

Sanders has endorsed Clinton, but some of his supporters protested in Philadelphia against the party leadership's apparent backing of her during the Democratic primary fight.

Sections of the convention hall were left conspicuously unpopulated on Tuesday night as delegates from strongly pro-Sanders delegations, including California, walked out after Sanders moved that Clinton be named the nominee.

(Feature image source: Twitter)