A prominent Vietnamese blogger known as 'Mother Mushroom' was jailed for 10 years on Thursday, her lawyer said, during a brief trial rights groups decried as "outrageous".

Nguyen Ngoc Nhu Quynh, whose pen name derives from her daughter's nickname "mushroom", was arrested in October 2016 and later charged with anti-state propaganda over critical Facebook posts about politics and the environment.

Vietnam's one-party state keeps a tight clamp on dissent and routinely jails activists, bloggers and lawyers who speak out against the communist regime.

The 37-year-old blogger faced a maximum of 12 years in prison, and her lawyer said the heavy sentence she received at the closed-door trial was "harsh".

"I am not happy with the result of the trial today," Nguyen Kha Thanh told AFP, adding that Quynh would likely appeal.

AFP was barred from attending the one-day trial in south-central Khanh Hoa province Thursday, which was heavily guarded by police, according to images on social media.

Thanh said Quynh was calm throughout the trial. In a pre-sentence statement she admitted no guilt and instead used the opportunity to send a message to her two kids and mother, the lawyer added.

"She apologised to her mother and the two kids for what effect this has had on them, but she said they must be very proud of her," Thanh told AFP.

- Woman of Courage award -

Quynh was charged under Article 88 of Vietnam's criminal code and held incommunicado with no access to lawyers until June 20, according to Thanh.

She has been a vocal critic of Vietnam's human rights record, civilian deaths in police custody and the government's handling of a toxic leak that killed tonnes of fish last year.

She was arrested in Nha Trang on October 10 as she was visiting a fellow activist in prison.

In the verdict, the judge said Quynh had defamed the government, harmed national unity, eroded popular trust of the government and undermined national security.

She was also convicted for publishing inaccurate information to humiliate the police and erode public trust in them, based on her reports about police brutality.

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Human Rights Watch earlier decried the trial as "outrageous" and demanded her release.

"The scandal here is not what Mother Mushroom said, but Hanoi's stubborn refusal to repeal draconian, rights-abusing laws that punish peaceful dissent and tarnish Vietnam's international reputation," Phil Robertson, HRW deputy Asia director said in a statement Wednesday.

The United States, Britain and the European Union have all called for Quynh's release.

Vietnam's Ministry of Foreign Affairs spokeswoman Le Thi Thu Hang said Thursday "all acts that violate the law will be seriously punished in accordance with Vietnamese laws" when asked about the case.

Quynh received an International Woman of Courage Award from the US State Department in March, which Vietnam said was "not appropriate and of no benefit for the development of relations between the two countries".

In 2015, she was awarded the Civil Rights Defender of the Year by a Sweden-based international advocacy group.