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New York billionaire Donald Trump has formally accepted the Republican Party nomination for president, vowing to defeat Democratic rival Hillary Clinton in November in the US general elections.

Trump "humbly and gratefully" accepted the presidential nomination on Thursday and joined the crowd in chants of "USA! USA!" at the Republican National Convention.

The former reality TV star and real estate mogul, who has never previously held elected office, blasted Clinton for her policies towards the Middle East and her willingness to accept Syrian refugees.

"After 15 years of wars in the Middle East, after trillions of dollars spent and thousands of lives lost, the situation is worse than it has ever been before. This is the legacy of Hillary Clinton: death, destruction, terrorism and weakness," he .

"My opponent has called for a radical 550 percent increase in Syrian refugees on top of existing massive refugee flows coming into our country under President Obama. She proposes this despite the fact that there's no way to screen these refugees in order to find out who they are or where they come from."

"We must immediately suspend immigration from any nation that has been compromised by terrorism until such time as proven vetting mechanisms have been put in place."

Trump also repeated his pledge to build a wall along the southern border with Mexico in a bid to stop illegal immigration and drug trafficking.

Clinton fired off a series of icy rebukes midway through Trump's sweeping acceptance speech.

The speech caps an extraordinary campaign that has defied political norms and marked a stunning primary victory for Trump.

According to an released on Tuesday, Trump has narrowed the gap with Clinton, the presumptive Democratic nominee, to 7 percentage points from 15 points.

Forty-three percent of likely voters supported Clinton in the July 15-19 poll, while 36 percent supported Trump.