Somewhat related, Chinese CDC posted their official guidance on mask usage. Google translate:

I. The general public

(1) Home and outdoor, no people gathered, well ventilated. It is not recommended to wear a mask.

(2) Being in a crowded place, such as office, shopping, restaurant, conference room, workshop, etc .; or taking a box elevator or public transportation. In low- and medium-risk areas, it is recommended that you wear spare masks (disposable medical masks or medical surgical masks) with you, and wear them when in close contact with other people (less than or equal to 1 meter). In high-risk areas, disposable medical masks are recommended.

(3) For those with cold symptoms such as coughing or sneezing. It is recommended to wear disposable medical or surgical masks.

(4) For those who live together with those who are separated from home and discharged from rehabilitation. It is recommended to wear disposable medical or surgical masks.

2. Personnel in specific places

(1) It is located in densely populated hospitals, bus stations, railway stations, subway stations, airports, supermarkets, restaurants, public transportation, and community and unit import and export places. In medium and low risk areas, it is recommended that workers wear disposable medical masks or surgical surgical masks. In high-risk areas, it is recommended that workers wear medical surgical masks or protective masks that comply with KN95 / N95 and above.

(2) In prisons, nursing homes, welfare homes, mental health medical institutions, school classrooms, construction site dormitories and other densely populated places. In medium and low-risk areas, it is recommended that you always wear spare masks (disposable medical masks or surgical surgical masks) with you daily, and wear masks when people gather or come into close contact with one another (less than or equal to 1 meter). In high-risk areas, it is recommended that workers wear medical surgical masks or protective masks that comply with KN95 / N95 and above; other personnel wear disposable medical masks.

Key personnel

Suspected cases, confirmed cases, and asymptomatic infections of new coronavirus pneumonia; close contacts of new coronavirus pneumonia; immigrants (from entry to end of quarantine). It is recommended to wear medical surgical masks or protective masks without exhalation valve that conform to KN95 / N95 and above.

Occupational exposure

(1) Medical personnel such as general outpatient clinics and wards; emergency medical personnel in medical institutions in low-risk areas; administrative personnel, police, security, cleaning, etc. engaged in epidemic prevention and control. Medical surgical masks are recommended.

(2) Personnel working in the ward and ICU of patients diagnosed with a new type of coronavirus pneumonia, suspected case patients; medical staff at designated medical institutions for fever clinics; medical staff in emergency departments of medical institutions in middle and high risk areas; epidemiological investigations and experiments Room testing, environmental disinfection personnel; transfer of confirmed and suspected cases. Medical protective masks are recommended.

(3) Operators engaged in the collection of respiratory specimens; staff who perform tracheotomy, tracheal intubation, bronchoscopy, sputum suction, cardiopulmonary resuscitation, or lung transplantation, pathological anatomy in patients with new-type coronavirus pneumonia. Suggestion: hood-type (or full-type) powered air-supply filter respirator, or half-plane power-supply air-filter respirator with goggles or full screen; P100 anti-particulate filter should be used for both types of respiratory protection Elements and filter elements should not be reused. Use protective equipment after disinfection.

https://zhuanlan.zhihu.com/p/114129365