Death registration data is unavailable or unusable for China due to quality issues. Estimates of mortality by cause should be interpreted with caution. These estimates may be used for priority setting, however, they are not likely to be informative for policy evaluation or comparisons among countries.

https://data.who.int/countries/156

We can also review an excerpt from the population introduction from the Chinese Statistical Yearbook, which the study someone cited above cites as their primary data source.

Data in this chapter are prepared by the Department of Population and Employment Statistics of the National Bureau of Statistics. In tables 2-1 to 2-6, figures for 1981 and before are from household registrations; data for the year 1982, 1990, 2000, 2010 and 2020 are the census year estimates; the rest of the data covered in those tables are estimates from the annual national sample survey on population changes and data for selected years have been revised