New York, New York - Hillary Clinton was greeted with a standing ovation during her surprise appearance at the 77th Tony Awards.

The former US secretary of state highlighted the historical importance behind the musical Suffs, which she co-produced, as she arrived on stage to introduce a musical number from the cast.

"I have stood on a lot of stages, but this is very special," the 76-year-old said.

"I know a little bit about how hard it is to make change, so I am extremely proud of this original American musical by Shaina Taub, two time tony winner."

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Clinton used the on-stage opportunity to emphasize the importance of voting ahead of the November election in which Donald Trump will face President Joe Biden.

"Of course it is about some American originals, the suffragists who fought so valiantly for so long to give women in our country the right to vote," she said.

"It is almost impossible to think about what a challenge that was, but now it is an election year and we need to be reminded about how important it is to vote."

Former First Lady Clinton lost the election in a shock defeat to Trump in 2016.

She recently went against New York's Congressman Jamaal Bowman by supporting his challenger, the more conservative George Latimer.

Suffs, a musical which follows suffragette movement and their "relentless pursuit of the right to vote," won two Tony awards for best original score and best book of a musical.