Mr Wu, who was a Catholic, died this morning while on holiday in Honduras, though the cause of his death is not yet known.
He experienced harsh work regimes, beatings, torture and near-starvation when he was sentanced to China's brutal prison camp system, known as laogai, in 1960 after criticising China's then-ally, the Soviet Union.
Released in 1979, Harry Wu moved to the USA in 1985 where he founded to Laogai Research Foundation but he made subsequent trips to China to research the labour camp system.
Mr Wu's Washington D.C.-based foundation established the Laogai Museum in 2008 to "preserve the memory of the laogai's many victims and serve to educate the public about the atrocities committed by China's communist regime."
Harry Wu wrote several books including The Chinese Gulag and other causes he campaigned for included labour rights, religious liberty, as well as an end to capital punishment and coercive organ harvesting.
Laogai and a milder version called laojiao ("reform through education") have since been abolished but the Chinese prison system continues to use penal labour.
Ben Rogers from Christian Solidarity Worldwide met Harry Wu and spoken with Premier earlier, saying: "We've lost Harry Wu but, at the same time, there are actually other courageous people - Christians and others - in China, on the ground, who are continuing speak out, particularly human rights lawyers who've suffered a very severe crackdown over the past year.
"He could easily have taken the decision to put it all behind him and lead a comfortable life in the West but he instead used the freedom that he had in the West to continue not only speaking out on China but also going back to China on several occasions to document the prison camps."
Ann Noonan from Harry Wu's Laogai Human Rights Organisation told the Associated Press by phone from New York: "He was a real hero. Harry's work will continue, it will not stop."