Former Australian prime minister Julia Gillard said the legacy of Ruth Bader Ginsburg endures, particularly her "determination to achieve gender equality".
"Ruth Bader Ginsburg’s intellect, wise words and determination to achieve gender equality shined throughout her long life of achievement," she wrote in a statement on Twitter.
"She inspired women around the world to do more and fight harder. RBG will be missed but her legacy endures."
Ms Ginsburg died on Friday at her home in Washington at the age of 87, after a battle with metastatic pancreatic cancer.
Ruth Bader Ginsburg spoke about her life and work during a discussion at Georgetown Law School in Washington on 6 April 2018. Source: AAP
She served 27 years as the US Supreme Court's second female justice.
Labor's spokesperson for education, Tanya Plibersek, said Ms Ginsburg's achievements have had a global impact.
"We are all indebted to her and her legacy," she wrote on Twitter.
Flowers and light candies outside the US Supreme Court to honour Justice Ruth Bader Ginsburg. Source: AAP
Mourners outside the court broke out in song, singing "Imagine" by John Lennon.
US Chief Justice John Roberts said the eight other justices of the court are saddened by the loss.
"Our Nation has lost a jurist of historic stature," he said.
"We at the Supreme Court have lost a cherished colleague. Today we mourn, but with confidence that future generations will remember Ruth Bader Ginsburg as we knew her - a tireless and resolute champion of justice."
'An amazing woman'
US President Donald Trump was campaigning in Minnesota when he found out about the death of the woman known by her admirers as "the Notorious RGB".
"She just died?" he told reporters. "I didn't know that."
"Whether you agreed or not, she was an amazing woman who led an amazing life," he added. "I'm actually saddened to hear that."
In a later statement, he expanded on his tribute.
"Today, our nation mourns the loss of a titan of the law" who was "renowned for her brilliant mind and her powerful dissents at the Supreme Court.
"Her opinions, including well-known decisions regarding the legal equality of women and the disabled, have inspired all Americans, and generations of great legal minds," he added.
During his remarks on the campaign trail, Mr Trump did not mention filling her vacant Supreme Court seat.
But her death just over six weeks before Election Day is likely to set off a heated battle over whether President Donald Trump should nominate, and the Republican-led Senate should confirm, her replacement, or if the seat should remain vacant until the outcome of his race against Democrat Joe Biden is known.
Mr Trump has told supporters he will pack the court with conservative-leaning justices for a generation to come if he defeats Mr Biden in November.
In August, Mr Trump told conservative radio talk show host Hugh Hewitt that he "absolutely" would fill a high court vacancy should an opportunity present itself before his first term expired.
Mourners gather on the steps of the US Supreme Court after Justice Ruth Bader Ginsburg died from pancreatic cancer in Washington, DC, USA, Source: AAP
Majority Leader Mitch McConnell said on Friday that the Senate will vote on Mr Trump's pick to replace Ms Ginsburg, even though it's an election year.
Flags were also lowered at the US Capitol at the direction of House Speaker Nancy Pelosi, the top Democrat and Mr Trump's chief nemesis in Washington.
"Justice Ginsburg embodied justice, brilliance and goodness, and her passing is an incalculable loss for our democracy and for all who sacrifice and strive to build a better future for our children," Pelosi said in a statement.
Former Democratic presidential candidate Hillary Clinton said her own achievements owed much to the trailblazing efforts of Ms Ginsburg.
"Justice Ginsburg paved the way for so many women, including me," she wrote on Twitter. "There will never be another like her. Thank you RBG."
Former US president George W. Bush said she "inspired more than one generation of women and girls", while former US president Jimmy Carter said he never regretted appointing her to the US Court of Appeals in 1980.
"A powerful legal mind and a staunch advocate for gender equality, she has been a beacon of justice during her long and remarkable career," he said. "I was proud to have appointed her to the US Court of Appeals in 1980."
Melinda Gates said Ms Ginsburg was a "force for equality and integrity" and a personal hero.
"She was a brilliant jurist, an inimitable Supreme Court justice, a force for equality and integrity—and she was one of my heroes. There will never be another RBG, but we are a much better, fairer country for all that she gave us."
Democratic vice-presidential nominee Kamala Harris said she would continue to fight for Ms Ginsburg's legacy.
"Tonight we mourn, we honor, and we pray for Justice Ruth Bader Ginsburg and her family. But we also recommit to fight for her legacy."
Additional reporting: AFP, AAP.
