A Chinese court convicted and jailed a 71-year-old journalist Friday for leaking state secrets in a decision condemned by rights groups as part of Beijing's widening "attack on freedom of expression".

Gao Yu -- named one of the International Press Institute's 50 "world press heroes" in 2000 -- "illegally provided state secrets to foreigners", Beijing's No. 3 Intermediate People's Court said on a verified social media account.

The ruling said Gao -- who was jailed for seven years -- had leaked a 2013 directive by the ruling Communist Party named "Document number 9" to a Hong Kong media outlet.

The document warns of the "dangers" of multiparty democracy, independent media, "universal" definitions of human rights and criticism of the party's historical record, according to copies widely circulated online.

"We are very disappointed with this verdict," said Shang Baojun, one of her lawyers, who argued in court that a "confession" from Gao had been extracted after threats were made against her son.

The US urged China to free Gao, describing her jailing as "part of a disturbing pattern" of oppression of anyone who questions Beijing's policies.

William Nee, a researcher for Britain-based Amnesty International, said Gao was "the victim of vaguely worded and arbitrary state-secret laws that are used against activists as part of the authorities' attack on freedom of expression".

Known for her outspoken support for democracy and press freedom, Gao went missing last April and resurfaced on China's state broadcaster a month later admitting she had made a "mistake".

Shang said the main evidence presented at Gao's trial in November was a "confession" she made after police threatened the journalist's son -- who they had also detained.

He added that after the verdict was read out Gao stated in a "strong voice" that she would appeal, but was not allowed to make any further statement.

The court denied the defence access to documents used to convict her, the lawyer said. The septuagenarian suffers from high blood pressure and Shang added he was "very worried" about her health.

Chinese courts are tightly controlled by the ruling party and more than 99 percent of defendants are convicted, with appeals rarely successful.

Police and security staff pushed foreign journalists hoping to cover the verdict more than 100 metres away from the courthouse, and bundled a Chinese individual into a police vehicle.

- 'Blow to free expression' -

China's President Xi Jinping has overseen a harsh crackdown against critics of the Communist Party, with scores of journalists, lawyers and academics detained and dozens jailed.

The country's definition of "state secrets" is notoriously broad, taking in the number of people executed each year, information about pollution, and databases listing commercial companies.

A consistent advocate for democracy and free speech, Gao was imprisoned following the government crackdown on student protests in Tiananmen Square in 1989.

Her political writings saw her jailed for six years in the 1990s, also on a charge of "leaking state secrets".

She was detained again in the lead-up to the Tiananmen crackdown's 25th anniversary last year, as were dozens of other government critics, and her one-day trial was conducted in secret.

Prosecutors said that a researcher affiliated with China's agriculture ministry gave Gao a copy of "Document number 9" in 2013, according to a copy of the verdict posted online by friends of Gao and confirmed to AFP by Shang.

The prosecution said she had used the online telecommunications tool Skype to transfer the document to Ho Pin, head of Hong Kong-based publishing house Mirror Books, one of many outlets which has released the text in the last two years.

Mirror Books denied receiving the document from Gao in a statement posted online Friday.

"This so-called 'secret document' is not concerned with military secrets, or even economic secrets. It is a mere guide to ideology," it said.

Gao's arrest "was part of an effort to intimidate and silence journalists and activists" ahead of the Tiananmen anniversary, the US chapter of free speech group PEN International said.

Beijing's foreign ministry spokesman Hong Lei said the case had been handled "in accordance with the law".

"This is a matter of China's internal sovereignty," he told reporters.

Ahead of the ruling, France-based Reporters Without Borders said it would be a gauge of "how far the Chinese authorities are ready to go in order to suppress those who speak with an independent voice".

The group ranked China 176th out of 180 countries in its 2015 Press Freedom Index.