Barack Obama warns voters: 'The fate of the republic rests on your shoulders'

Hillary Clinton painted a grim picture of life under a Donald Trump presidency, warning undecided voters as the ever tighter White House race entered its final five-day stretch.

Clinton made an optimistic choice in staging a huge rally in Arizona, a swing state she hopes to poach from the Republicans, but the Democrat's tone was grim as she invited voters to envisage her defeat.

"Imagine it is January 20, 2017 and imagine that it is Donald Trump standing in front of the Capitol," she told a 15,000-strong crowd in Tempe, triggering a chorus of boos for her Republican opponent.

"Imagine that he is taking the oath of office and then imagine that he is in the Oval Office making the decisions that affect your lives and your future," she said.

Clinton painted a picture of Trump as a president who demeans women, exacerbates racial divisions and is so thin-skinned and unpredictable that he could "start a real war instead of a Twitter war."

The note of caution was echoed by President Barack Obama, who warned voters that America's very future was at stake. He will duel with Trump on Thursday when they hold rival rallies in Florida.

"The fate of the republic rests on your shoulders," he declared in North Carolina, one of a handful of swing states where the race will be decided.

"The fate of the world is teetering and you, North Carolina, are going to have to make sure that we push it in the right direction," Obama declared.

The 70-year-old Republican, by contrast, treated supporters in Florida to a now familiar tirade, predicting Clinton's downfall and vowing to "drain the swamp" of corruption in Washington.

Appearing before fans at a triumphal rally in Pensacola, Trump stuck closely to his well- rehearsed stump speech focused on his "contract with America, a plan to end government corruption."

And he boasted that many opinion-makers and voters are now flocking to his standard.

"We're only left with one person, crooked Hillary Clinton. We're going to win. We're going to win."

Such talk -- partly supported by one poll on Tuesday showing him moving slightly ahead of Clinton -- has delighted America's foes, made its allies queasy and spooked financial markets.

Trump has been battered by scandals that would have sunk a less brazen showman: accused of sexual assault, of not paying taxes and of ties to Russia's Vladimir Putin and the mob.

But renewed FBI scrutiny of Clinton's use of a private email server when secretary of state has fired up the Republican's raucous fan base and fed doubts about the Democrat's trustworthiness.

- Foregone conclusion -

US markets have not responded well. The Dow fell 0.4 percent and the broader S&P 500 was off 0.7 percent at the close. Earlier major markets in Asia and Europe had tumbled more than one percent.

The dollar continued to slip against the euro, losing 0.3 percent to $1.1093, while the Mexican peso -- sensitive to Trump's threat to build a wall on the country's border -- lost one percent.

The dramatic tightening in the opinion polls also frightened bookmakers. Ireland's Paddy Power had already paid out $1 million to punters who bet on Clinton, assuming her victory a foregone conclusion.

But on Wednesday, the firm said 91 percent of bets now favor Trump, whose odds have narrowed.

This week, US Secretary of State John Kerry admitted the campaign has been "downright embarrassing" as he deals with America's friends and foes abroad, and the latter are in full voice.

Iran's supreme leader Ayatollah Ali Khamenei -- whose regime paints America as a comic-book foe -- crowed that the "catastrophic reality" of the candidates "goes beyond what even we were saying."

In Britain, a giant effigy of Trump wielding the head of his rival Clinton was to be burned during traditional November 5 bonfire night celebrations.

- Long-shot bets -

The long and often unedifying 2016 race is now being fought in a few corners of a few states, most notably Florida, Ohio and North Carolina.

These three states offer the best chance for both candidates to cross the winning threshold of 270 out of 538 electoral college votes.

But the two hopefuls have also placed some final long-shot bets.

Clinton traveled to Arizona, which Democrats haven't won since 1996 when her husband Bill claimed the presidency by a landslide.

An Emerson poll on Wednesday had Clinton losing the state by only four percentage points, and both of its Republican senators oppose Trump, offering the prospect of a shock Clinton win.

Meanwhile, Trump has raised eyebrows by campaigning in Wisconsin and Michigan, both traditionally Democratic states where polls show Clinton leading by six points or more.

And he spent most of Wednesday in Florida -- which is likely to make-or-break his presidential dreams -- and was to remain there Thursday seeking to build momentum before the dash for the finish line.