Obama will highlight Clinton's toughness to lead

President Barack Obama formally endorsed Hillary Clinton's bid for the White House on Thursday, praising his former secretary of state's experience and grit, and urging Democrats to unite behind her in the fight against Republicans in the fall.

Barack Obama will highlight Hillary Clinton's judgment and toughness to boost her campaign to be the first woman to become US president, hoping to hand over the White House to a trusted fellow Democrat and stop Republican Donald Trump.

Clinton formally secured the Democratic Party's presidential nomination at the party's convention in Philadelphia yesterday.

She will accept the nomination on the last day of the meeting tomorrow, becoming the Democratic standard-bearer against Trump in the November 8 election.

Today's convention events will focus on national security, looking to contrast the 68-year-old former Secretary of State's skills with Trump's "unsteady, unfit and dangerous approach," said Clinton campaign chair John Podesta.

In a highly unorthodox move, Trump appealed to Russia today to uncover and release thousands of emails that Clinton did not hand over to US officials as part of a probe into the use of her private email system while she was the country's top diplomat from 2009-2013.

Clinton has said the emails she did not hand over were private. Trump, a 70-year-old New York businessman with no experience in political office, has hammered Clinton as untrustworthy and cast America as a place where security threats abound and law and order are breaking down.

He has proposed deeply controversial measures such as temporarily banning Muslims from entering the country and building a wall on the Mexico border to stop illegal immigrants.

The Clinton campaign portrays Trump, a former reality TV star, as temperamentally unfit for the White House.

"I hope my headline (from the speech) is that the President of the United States is profoundly optimistic about America's future and is 100 per cent convinced that Hillary Clinton can be a great president," Obama said in an interview with NBC News broadcast today, ahead of his speech this afternoon.

Obama "has been candid about why he thinks electing the Republican nominee is a risky path for the United States," White House spokesman Eric Schultz said.

However, Obama's speech would focus more "on how Secretary Clinton has the judgment, the toughness and the intellect to succeed him in the Oval Office," Schultz said.

THE AFTERNOON SESSION
Former Congressman and Secretary of Defence Leon Panetta
US Senator Sherrod Brown of Ohio
Vice-President Joe Biden
Atlanta Mayor Kasim Reed
Former New York Mayor Michael Bloomberg
Musical Performance: Lenny Kravitz
Democratic Nominee for Vice-President Tim Kaine
President Barack Obama

As well as Obama, speakers today will include Clinton's vice presidential running-mate, Tim Kaine, Vice-President Joe Biden, former New York Mayor Michael Bloomberg and Leon Panetta, a former Defence Secretary and former head of the CIA.

Also appearing are actress Sigourney Weaver, director Lee Daniels and actress Angela Bassett. Rocker Lenny Kravitz will perform.

After being formally nominated yesterday, Clinton got a warm endorsement from her husband, Bill Clinton. The former President called his wife, who has also been a US senator, a dynamic force for change and sought to paint his wife in a warm personal light.

- Reuters, AAP