The head of the World Health Organization (WHO) is being censored on China's internet after questioning the sustainability of the country's zero-Covid policy.

The censorship on Weibo and WeChat, China's two largest social media platforms, targets WHO Director-General Tedros Adhanom Ghebreyesus' comments that expressed rare disagreement with Beijing's policies.

"When we talk about the zero-Covid strategy, we don't think that it is sustainable, considering the behavior of the virus now and what we anticipate in the future," Tedros told a media briefing Tuesday, citing the increased transmissibility of Omicron.

"We have discussed this issue with Chinese experts and we indicated that the approach will not be sustainable...I think a shift will be very important," he said.

The criticism from Tedros, who was accused of being too close to China earlier in the pandemic, came just days after Chinese leader Xi Jinping vowed to double down on the policy and "resolutely struggle" against all critics.

The United Nation's official press account on China's Twitter-like Weibo posted Tedro's comments early on Wednesday morning, drawing a wave of sarcastic comments from Chinese users.

"Resolutely fight against any words and acts that distort, doubt, or deny our country's epidemic prevention and control policies! Down with the World Health Organization!" a top reply said.

"Should the UN's verified account be blocked this time?" another said.

By mid-morning, the post was no longer viewable on Weibo "due to the author's privacy setting." It is unclear under what circumstances the setting was changed.

A Weibo hashtag of Tedros' name has also been censored, with images featuring his face being scrubbed from the platform, though posts containing his name are still visible.

On WeChat, an article from the UN's official account that included Tedros' comments has been "banned from sharing due to a violation of relevant laws and regulations" as of Wednesday morning. Video clips of Tedros' speech have also been removed from the platform.

Tedros' comments, though in line with the assessment of most scientists, have also drawn the ire of Beijing, which called them "irresponsible."

"We hope relevant people can view China's epidemic prevention and control policy in an objective and rational way, learn more about the facts and refrain from making irresponsible remarks," Chinese Foreign Ministry Spokesperson Zhao Lijian said at a news briefing Wednesday.

China's zero-tolerance approach of snap lockdowns, mass testing, and quarantining has protected the majority of its population from Covid over the past two years, but it has drawn rising dissent as the lockdowns become more stringent and frequent amid the fast spread of Omicron.

Shanghai, the country's most populous and cosmopolitan city, is reeling from a six-week lockdown that has sparked public outcry, while the capital Beijing has shut schools, and restaurants and rolled out frequent mass testing to curb its outbreak. Elsewhere, more local governments are imposing swift lockdowns in response to just a handful of cases.

But the Chinese leadership has insisted on the strict measures, saying a relaxation will "inevitably lead to large scale infections, a large number of serious illness and deaths" due to the country's large number of elderly people and insufficient medical resources.

New modeling by researchers mostly from Shanghai's Fudan University predicted China could face over 1.5 million Omicron deaths if its zero-Covid measures are lifted without increased vaccine coverage or access to antiviral therapies.

Released Tuesday by the journal Nature Medicine, the peer-reviewed study found that based on immunity levels as of March, an unchecked Omicron wave would exceed critical care capacity across the country, causing 112.2 million symptomatic cases.

The research estimates that in the event of an uncontrolled Omicron outbreak, China's national healthcare system would be completely overwhelmed, with demand for the country's 64,000 ICU beds outstripping supply 15.6-times over, for a period of at least 44 days.

But that scenario could be avoided, according to the modeling, if the Chinese government focuses on increasing "accessibility to vaccines and antiviral therapies."

More than 88% of Chinese people have been fully vaccinated, but immunization is much lower among the elderly. As of March 17, only half of the people aged over 80 in China have been fully vaccinated, and less than 20% of that vulnerable age group have received a booster. Unlike most countries, elderly people were not originally prioritized in China's vaccination campaigns.

Since the latest outbreak, Chinese officials have vowed to speed up vaccination among the elderly. But in locked-down areas, it is virtually impossible to get vaccinated as residents are confined to their homes and allowed to go out only for Covid testing.