High-profile Vietnamese blogger "Mother Mushroom" has been released from prison and is en route to the United States, according to friends and human rights organisations.

Key points: Nguyen Ngoc Nhu Quynh frequently blogged about human rights including deaths in police custody

Nguyen Ngoc Nhu Quynh frequently blogged about human rights including deaths in police custody She is expected to arrive in the United States with her children

She is expected to arrive in the United States with her children More than 100 political prisoners are behind bars in Vietnam for "speaking their minds"

Nguyen Ngoc Nhu Quynh, known by the moniker Me Nam (Mother Mushroom), was arrested in October 2016 and sentenced to 10 years in prison for "conducting propaganda against the state".

Ms Quynh frequently blogged about human rights and the environment, and was outspoken on land grabs, deaths in police custody and freedom of expression.

Sources with direct knowledge of the matter said Mother Mushroom had departed Vietnam for the United States with her children and mother.

Her friend, Nguyen Tin, took to Facebook to celebrate that Mother Mushroom was reunited with her family in a free country after numerous efforts to secure her release.

Nguyen Ngoc Nhu Quynh was sentenced to 10 years in prison on charges of defaming the Communist government. ( AP: Tien Minh )

Bangkok-based Grace Bui, who has campaigned for human rights in Vietnam and worked with Mother Mushroom in the past, welcomed the news for the sake of Ms Quynh's two young children.

But she stressed there were scores more jailed in Vietnam without as high a profile.

"They don't release people unconditionally — I have never seen it," Ms Bui said.

"They use these activists like pawns, to trade something.

"We need to speak up for the people who are in jail right now — if one or two people get out, it doesn't mean that it's a good thing … we need to get the rest out because they are not criminals."

One of those activists is environmental activist Le Dinh Luong, who was sentenced to 20 years in prison for taking part in activities to "overthrow the state", and human rights defender Tran Thi Nga, jailed for nine years with an additional five years of house arrest for sharing articles about political corruption.

Vietnam's Foreign Ministry and its embassy in Australia have been approached for comment.

More than 100 'prisoners of conscience' remain in jail

Human Rights Watch and Amnesty International have campaigned for her release during her two-year incarceration, as has her 11-year-old daughter Nam.

"My mother is a good person and she always wants to protect other people," Nam told the ABC last year.

Ms Quynh received an International Woman of Courage Award, presented by US First Lady Melania Trump, in 2017, but Ms Quynh could not accept it as she was in pre-trial detention.

Her release coincided with US Defence Secretary Jim Mattis's visit to Vietnam.

Phil Robertson, from Human Rights Watch, said in a statement Mother Mushroom's release laid bare Vietnam's methods for dealing with dissenters.

"This release makes Vietnam's new political repression strategy clear: arrest activists on bogus, rights-abusing charges, prosecute them in kangaroo courts, and sentence them to ridiculously long prison terms," he wrote.

"Then, when hope fades in the face of years in horrific conditions behind bars, offer a freedom for exile deal and claim credit for the release."

Vietnamese political prisoner Mother Mushroom holds up a sign. ( Facebook: Nguyễn Ngọc Như Quỳnh )

No one should forget, he added, that "Vietnam is still one of the most repressive states in South-East Asia, with more than 100 political prisoners behind bars for speaking their minds".

The Committee to Protect Journalists said a friend of her family planned to meet her in Houston, Texas, when her flight touched down.

That source said Ms Quynh plans to live as an exile.

While the terms of her freedom are not confirmed, some reports suggest that leaving Vietnam was a condition of her release.