World Health Organization director-general Tedros Adhanom Ghebreyesus said in Geneva that the numbers "must be interpreted with extreme caution", adding: "This outbreak could still go in any direction".
Since its emergence in the central province of Hubei in December, the COVID-19 virus has killed more than 1,350 people and infected tens of thousands. "We have a window of opportunity to shut this virus down".
"The General Office of the National Health and Health Commission and the Office of the State Administration of Traditional Chinese Medicine issued the "Diagnosis and Treatment Plan for Pneumonia of New Coronavirus (Version) "adds" clinical diagnosis "to the case diagnosis classification in Hubei Province", the statement reads".
Excluding cases confirmed using the new methods, the number of new cases rose by only 1508, the official data showed.
There have been more than 500 infections in nearly 30 countries and territories outside mainland China, including two deaths.
The biggest cluster of cases outside China is aboard the Diamond Princess cruise ship quarantined off Japan's port of Yokohama, with about 3,700 people on board.
It was "an example of the worldwide solidarity we have consistently been calling for", he said.
Local authorities in Hubei and Wuhan had already faced rare, uncensored criticism online for initially downplaying the magnitude of the outbreak.
Authorities in Hubei have been accused of concealing the gravity of the outbreak in early January because they were holding key political meetings at the time.
Travel restrictions that have paralyzed the world's second-biggest economy have left Wuhan and other Chinese cities resembling ghost towns. The Dow industrials, S&P 500 and Nasdaq all hit new highs, and Asian shares nudged higher on Wednesday.
WHO, which has declared the coronavirus outbreak as a global health emergency, further stated that it poses a "very grave threat for the rest of the world" and should be viewed as "Public Enemy Number 1".
China will stagger the re-opening of schools to stave off virus risks, a government official said.