Democratic power players Michelle Obama and Bernie Sanders offered contrasting heartfelt and hard-headed endorsements of Hillary Clinton Monday, imploring a riven and feisty party convention to unite against Donald Trump.

As polls showed Trump ahead of Clinton in the race to the White House, the first lady wowed the Philadelphia crowd as she impeached Trump's character and hailed the inspirational power of putting a female US president in the White House for the first time.

From Sanders, Clinton's vanquished primary rival, there was a much more pragmatic embrace.

"Based on her ideas and her leadership" Clinton was a better choice than Trump and "must become the next president of the United States," he said.

(AFP)