Zhang Zhan was detained in May 2020 for her coverage of China's initial response to the Covid-19 outbreak, and served four years in prison for "picking quarrels and provoking trouble" -- a charge routinely used by authorities to suppress dissent.

The 42-year-old was detained again in August 2024 on the same charge, according to rights groups.

Her trial was due to take place on Friday at 9:00 am (0100 GMT) in Shanghai, Reporters Without Borders (RSF) and other groups said in statements this week.

"For the past year, (Zhang) has been cut off from the outside world, and almost all information about her whereabouts has been kept secret to prevent the international community from taking action against the appalling conditions in which she is being held," RSF said in their statement.

Outside the court on Friday, when asked if the trial was taking place, officials said: "On this case, we are not accepting media interviews."

A group of seven diplomats from European and North American countries who had requested to observe Zhang's case were also turned away, on the grounds that their paperwork was not in order, AFP saw.

Officials did not give the diplomats a clear confirmation or denial as to whether the trial was happening.

As 9:00 am approached, the police presence around the court increased, but AFP could not confirm whether the trial took place or if Zhang was present.

Zhang, a former lawyer, travelled to the central city of Wuhan in February 2020 to report on the chaos at the pandemic's epicentre, questioning the authorities' handling of the outbreak in her smartphone videos.

After being released from jail in May 2024, she was believed to be living in Shanghai under heavy surveillance.

In August 2024 she was detained again, for spreading "false information that seriously damaged the national image" on foreign social media, according to documents shared on X by Jane Wang, a UK-based activist.

In January, rights groups said Zhang had gone on hunger strike and was being force-fed through a gastric tube.