Hillary Clinton and Donald Trump will face off for the first time later today in a presidential debate that is one of the most highly anticipated political showdowns in US history.
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The gap between the two candidates in recent national opinion polls has narrowed in the past week, with the latest polling showing Clinton ahead by 4 percentage points.
The duel at Hofstra University could be the most watched debate in television history.
Ahead of the debate, the stock market on Monday showed jitters with Wall Street's "fear gauge," up 14 percent in early afternoon trading.
The debate begins at 2pm today NZT.
On Monday, Mr Trump's campaign manager Kellyanne Conway told MSNBC that the "natural connective tissue he has with people" will be on show.
"I can see that this man is ready for tonight," she added.
Meanwhile, Mrs Clinton's campaign manager Robby Mook told NBC's Today show that their camp hoped Mrs Clinton would come out on top on "the fine points of policy," but that they were concerned Mr Trump would get "the most improved award".
"Donald Trump is an experienced reality show entertainer so he may decide this is a chance to show his chops," he added.
The debate will last 90 minutes and is being moderated by NBC news anchor Lester Holt.
It is the most hotly anticipated event so far in a long election campaign, partly due to the contrasting styles of the two candidates.
As hotel developer and reality TV star, Mr Trump marched to a stunning win in the Republican primaries against vastly more experienced political opponents, he hurled personal insults and made suggestive remarks on the debate stage.
Mrs Clinton, with decades of experience in politics, usually relies more on a firm and detailed policy grasp, but has problems portraying authenticity and spontaneity.
Observers predict the audience could be as high as that for the Super Bowl and surpass the 80 million who watched Jimmy Carter and Ronald Reagan debate in 1980.
Controversy has marked the debate build-up after Mr Trump said he might invite a woman who had an affair with Bill Clinton in the 1970s.
He tweeted on Saturday that he would perhaps ask Gennifer Flowers to sit in the debate audience, in response to Mrs Clinton having invited billionaire Trump critic Mark Cuban.
Ms Flowers initially said she would attend but Mr Trump's running mate, Mike Pence, said on Sunday she was not coming and the suggestion was not a serious one.
Three of the topics for the six segments of the debate have already been announced - America's Direction, Achieving Prosperity and Securing America - but three others, based on events in the news, will be asked during the debate.
In the past week both candidates have focused on the response to fatal police shootings of African-American men in Tulsa, Oklahoma, and Charlotte, North Carolina, as well as the ensuing protests.
The second debate will be held on 5 October, and the third and final debate will be held on 20 October.