Phil Roberston, deputy Asia director at Human Rights Watch, said that Quang would be remembered for "a multi-year crackdown on human rights and putting more political prisoners behind bars in Vietnam than any time in recent memory".
The official Vietnam News Agency says Quang died at the 108 Military Hospital in Hanoi on Friday due to a serious illness. The reports did not provide further information about Quang's illness.
Quang passed away at a miliary hospital in Hanoi.
"He began showing symptoms of illness in June past year and has been treated in Japan six times since", Trieu told Reuters.
The Presidential position in the Vietnam government is largely considered ceremonial, but is one of the three highest-ranking positions alongside the Party General Secretary and Prime Minister.
In contrast to his reputation as tough and influential in the inner circles of the communist party, Quang, a member of the Politburo, often appeared uncomfortable in the public eye, and would read prepared scripts.
Before that, he had served as Minister of Public Security, an organisation with broad powers and a remit that includes intelligence gathering and thwarting domestic and foreign threats to the party.
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Quang had not been seen in public for several weeks before his death was announced.
"We are saddened to hear the news that the president has died", said Bui Duc Phi, council chairman of the village where he was born.
Rumours of Quang's illness had been swirling on social media for months.
Since last week, Quang had appeared thin and pale in public and unstable on his feet when he hosted a welcoming ceremony for visiting Indonesian President Joko Widodo in Hanoi.
Vietnam's constitution provides for the vice president to perform the president's duties should he be unable to work.
The national assembly is set to meet in late October, but the date could be brought forward, he added.