Watch: Donald Trump casts his vote with wife Melania

Republican candidate Donald Trump said he felt "very confident" in his campaign after casting his ballot alongside his wife, Melania, on Tuesday.

"It looks like Republicans have shown up in force", he told reporters at Palm Beach, Florida.

"I hear we're doing very well," he added.

Asked if he would concede defeat if he lost, he said he would do so "if it's a fair election".