President Donald Trump said he felt good about his chances for victory as US election day opened Tuesday, predicting that he would register big wins in key states such as Florida and Arizona.

"We feel very good," a hoarse-voiced Trump told Fox News in a phone interview. 

Trump said he expected victory in all the key states that will decide the election, but said he would not "play games" by declaring his win too early.

"We think we are winning Texas very big. We think we are winning Florida very big. We think we are winning Arizona very big," he said.

"I think we are going to do very well in North Carolina. I think we are going to do well in Pennsylvania. We think we are doing very well everywhere."

Running behind in most opinion polls, Trump bashed Democratic opponent Joe Biden, "biased" media and the "extreme" left as he repeated his argument for reelection to four more years in the White House.  

"Joe Biden is not prime time" he said.

Trump called it "terrible" and "dangerous" that millions of votes mailed in might still not be counted on Wednesday.

But he downplayed allegations that he planned to prematurely declare victory Tuesday evening before enough of the vote is tallied to determine the winner.

"I think we'll have victory, but only when there's victory," he said.

"Theres no reason to play games."