China on Saturday harshly criticised the United Nations over comments demanding the release of a citizen journalist jailed for her coverage of the country's COVID-19 response.

The Chinese mission in Geneva voiced outrage at the "irresponsible" and "erroneous" comments made by the United Nations human rights office OHCHR on Friday in the case of Zhang Zhan.

OHCHR spokeswoman Marta Hurtado on Friday voiced alarm at reports that the 38-year-old's health was deteriorating rapidly and that her life was at serious risk from the hunger strike in detention.

"We call on the Chinese authorities to consider Zhang's immediate and unconditional release, at the very least, on humanitarian grounds, and to make urgent life-saving medical care available, respecting both her will and her dignity," Hurtado said in a statement.

Zhang, a former lawyer, travelled to 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.

She was detained in May 2020 and sentenced in December to four years in jail for "picking quarrels and provoking trouble" -- a charge routinely used to suppress dissent.

She has conducted several hunger strikes to protest against her conviction, sentencing and imprisonment, and her family recently warned that she had become severely underweight and "may not live for much longer".

'Hearsay'

Hurtado said the UN rights office had repeatedly raised concerns over Zhang's case with the Chinese authorities since her arrest last year.

It had sought "clarification on the criminal proceedings taken against her as a consequence of what appear to have been her legitimate journalistic activities", she said.

China has revelled in its success in keeping domestic Covid infections down to a trickle of sporadic outbreaks.

But there has been little patience with those who threaten the official version by raising questions about the government's early handling of the Wuhan outbreak.

Zhang is among a group of four citizen journalists -- along with Chen Qiushi, Fang Bin and Li Zehua -- detained after reporting from Wuhan.

In Saturday's statement, Chinese mission spokesman Liu Yuyin insisted that "China is a country under the rule of law, and everyone is equal before the law."

He decried that the UN rights office in Zhang's case had turned "a blind eye to information provided by China through normal channels," and instead, "based on hearsay, chose to interfere in China's judicial sovereignty."

He also highlighted China's response to COVID-19, insisting that what the country "has achieved in combating the pandemic is there for everyone to see."

It "is not something that anyone can distort or write off, still less something that the OHCHR can throw its weight around."