Nearly 90% of people in Henan, China's third most populous province, have now been infected with Covid, local health officials say.
Provincial official Kan Quancheng revealed the figure – amounting to about 88.5 million people – at a press conference.
China is battling an unprecedented surge in cases after abandoning zero-Covid policies in December.
The move followed rare protests against lockdowns, quarantines and mass tests.
Mr Kan did not specify a timeline for when all the infections happened – but as China's previous zero-Covid policy kept cases to a minimum, it's likely the vast majority of Henan's infections occurred in the past few weeks.
He said visits to fever clinics in Henan province peaked on 19 December "after which it showed a continuous downward trend".
The Henan provincial figures are in stark contrast to Covid figures from the central government
According to official data, just 120,000 people in the country of 1.4 billion have been infected and 30 died since the shift in Covid policy.
Meanwhile on Sunday, authorities reported three Covid deaths in mainland China, one more than the day before.
However, with the definition of Covid deaths narrowed and mass testing no longer compulsory, government data is no longer reflective of the true scale of the outbreak.
Other local and provincial officials have also been providing very different data to that from the central government. On Christmas Eve, a senior health official in the port city of Qingdao reported that half a million people were being infected each day. Those case figures were swiftly removed from news reports.
Meanwhile Chinese health officials said they would not include Pfizer's antiviral Covid medicine Paxlovid in its basic medical insurance schemes as a result of the high price quoted by the US firm.
The drug, temporarily covered by China's broad healthcare insurance scheme until 31 March, has seen a sharp increase in demand since China's Covid cases surged last month.
Pfizer would continue to collaborate with the Chinese government and all relevant stakeholders to "secure and adequate supply" of the medicine in China, the company said in a statement.
On Sunday, Beijing also lifted mandatory quarantine for all international arrivals and opened its border with Hong Kong.
In the first wave of pre-holiday travel, official data showed that 34.7 million people travelled domestically on Saturday. This represented an increase of more than a third compared to last year, according to state media.
Infections are expected to soar as the country celebrates Lunar New Year later this month, with millions expected to travel from big cities to visit older relatives in the countryside.
Overall, more than two billion individual journeys are expected to take place, officials have said.
Listen to more on what we know about China's Covid numbers: More or Less- Behind the Stats – Can China's data on Covid deaths be trusted- on BBC Sounds
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