Trump and Clinton began their first face-off Monday in what many pundits presumed would be the most-watched debate in history ahead of the November 8 election.

The two clashed over plans for growing US economy, with Clinton accusing him of pushing economic policy that favored the rich at the expense of the middle class.

"The kind of plan that Donald has put forth would be trickle-down economics all over again. And in fact it would be the most extreme version, the biggest tax cuts for the top percents of the people in this country that we've ever had. I call it Trumped-up trickle-down, because that's exactly what it would be. That's not how we grow the economy," she said.

Trump criticized Clinton for her trade policies, saying she has had decades without making lives better for Americans.

"We have to renegotiate our trade deals and we have to stop these countries from stealing our companies and our jobs," he said.

Trump said Clinton's economic plan is "all talk, no action, sounds good, never going to work."

He attacked Clinton over her use of a private email server as secretary of state and she criticized Trump for not releasing his tax history.

US Democratic presidential nominee Hillary Clinton speaks during the Presidential Debate at Hofstra University on September 26, 2016 in Hampstead, New York. (Photo by AFP)

“I'm not going to make any excuses, it was a mistake,” Clinton said referring to her use of private email.

She also said Trump is “trying to hide” his tax history, adding, "it must be something really important, even terrible.”

Trump reacted by saying, "I will release my tax returns against my lawyer's wishes when she releases her 33,000 e-mails that have been deleted."

Clinton also accused Trump of having a "long record of engaging in racist behavior" and criticized him for putting into question the citizenship of President Barack Obama.

"He has really started his political activity based on this racist lie that our first black president was not an American citizen. There was absolutely no evidence for it. But he persisted. He persisted year after year," Clinton said.

US Republican presidential nominee Donald Trump speaks during the Presidential Debate at Hofstra University on September 26, 2016 in Hampstead, New York. (Photo by AFP)

Trump, in response, raised Clinton's tough critiques of Obama during their 2008 primary battle.

"You treated him with terrible disrespect and I watch the way you talk now about how lovely everything is, ... it doesn't work that way."

"When you try to act holier than thou, it really doesn't work," the business mogul added.

On Daesh, Trump blamed Obama and Clinton for creating the terrorist group after the US pulled out its troops from Iraq, leaving “a vacuum the way they got out of” the country.

“They wouldn’t have even been formed if they left some troops behind,” Trump said.

Trump, however, did not reveal his plan for defeating Daesh, with Clinton saying, he had no plan at all.

"Well, at least I have a plan to fight ISIS (Daesh)," Clinton said, noting the US needs to intensify US air strikes against Daesh and work with Turkish and Kurdish forces to fight the terrorists.

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