Democratic National Convention begins in disarray

The Democratic National Convention opened to chaotic scenes on Monday, as rival supporters of Hillary Clinton and Bernie Sanders traded boos, jeers and taunts in a very public show of party disunity.

While shock polls showed Republican Donald Trump leading the race for the White House, Democrats gathering in Philadelphia to make Clinton the first woman presidential nominee from a major party appeared in disarray.

Sanders supporters booed when a pastor leading the invocation prayer thanked God that Clinton was the nominee, setting the stage for each successive mention to spark a raucous chorus of outbursts. 

Twice on Monday, Sanders appealed to supporters to help build party unity, ahead of a pivotal primetime address to delegates. 

"We have got to defeat Donald Trump. We have got to elect Hillary Clinton and (running mate) Tim Kaine," Sanders told a gathering of his supporters. 

"Trump is a bully and a demagogue," he said. His call to support Clinton was nevertheless met with loud jeers.

He later sent a text message to supporters asking them not to protest on the floor of the convention as a "personal courtesy" to him. 

But that appeared to have minimal impact, with boos erupting at the very mention of Clinton's name, followed by Clinton supporters chanting "Hillary! Hillary!" over them.

The boos were minimised, however, when popular First Lady Michelle Obama and left-wing Senator Elizabeth Warren took the stage for speeches.

The party is reeling from leaked Democratic National Committee emails that show nominally neutral party staff trying to undermine Sanders' campaign and questioning his Jewish faith.

WikiLeaks at the weekend released nearly 20,000 emails from between January 2015 and May 2016, gleaned by hackers who apparently raided the accounts of seven DNC leaders.

The Federal Bureau of Investigation said it was investigating the "cyber intrusion," which the Clinton campaign blamed on Russian hackers bent on helping Trump.

Sanders, a self-proclaimed democratic socialist who promised a "political revolution" lost to Clinton in the primary.

But the scandal has angered his already embittered supporters, who believe the deck was stacked against them. 

It has led to the resignation of Democratic Party chair Debbie Wasserman Schultz and an apology from party leaders.

"We want to offer a deep and sincere apology to Senator Sanders, his supporters, and the entire Democratic Party for the inexcusable remarks made over email," the Democratic National Committee said in a statement.

Clinton announced last Friday that she has chosen Tim Kaine, a Catholic senator from the battleground state of Virginia, to be her White House running mate.

"I'm thrilled to announce my running mate, @timkaine, a man who's devoted his life to fighting for others. -H," the presumptive Democratic nominee tweeted.

Kaine, who currently serves on the Senate Foreign Relations and Armed Services committees, could help Clinton bring in two key voting blocs: Hispanics and the battleground state of Virginia.

But Kaine, a centrist who is seen as close to Wall Street, has little to appeal for Sanders supporters.