According to a report by the World Health Organization (WHO), China has taken many measures against the spread of the Coronavirus. They launched a national emergency response and created the Central Leadership Group for Epidemic Response and the Joint Prevention and Control Mechanism as a part of this national emergency. This report also states there have been three main phases of responses taken to contain COVID-19.
The first phase focuses on preventing the spread of cases and other areas where COVID-19 has rapidly spread, into places where there are not as many cases. They closed markets and began investigating into the source of Coronavirus. They reported this to WHO on January 3, and also reported the genome sequences of COVID-19 to WHO on January 10.
The second phase was intended to "reduce the intensity of the epidemic and to slow down the increase in cases." They wanted to treat the cases and further prevent the spread of COVID-19. They implemented traffic controls, transportation controls, extending the Spring Festival holiday, strengthening education about the disease, and trying to maintain supply of necessary goods and items.
The third phase was mainly focused on reducing the number of cases and controlling the pandemic. They thoroughly focused on treating patients and preventing transmission. They adopted a highly controlled approach on social operations.
Quoted from WHO, "China has rolled out...the most ambitious, agile and aggressive disease containment effort in history." WHO further discussed that China has been thoroughly promoting and enforcing the monitoring of temperature, wearing medical face masks, and washing hands often.
You can learn more about the strategies China has taken concerning the COVID-19 pandemic at https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-report.pdf