BackgroundSince the outbreak of COVID-19, the Chinese government and the Chinese Center for Disease Control and Prevention have released COVID-19–related information to the public through various channels to raise their concern level of the pandemic, increase their knowledge of disease prevention, and ensure the uptake of proper preventive practices. ObjectiveOur objectives were to determine Chinese netizens’ concerns related to COVID-19 and the relationship between their concerns and information on the internet. We also aimed to elucidate the association between individuals’ levels of concern, knowledge, and behaviors related to COVID-19. MethodsThe questionnaire, which consisted of 15 closed-ended questions, was designed to investigate Chinese netizens’ knowledge about COVID-19. The self-selection online survey method of nonprobability sampling was used to recruit participants through Dingxiangyisheng WeChat (a public, medical, and health service platform in China) accounts. Standard descriptive statistics and multivariate logistic regression analyses were conducted to analyze the data. ResultsIn total, 10,304 respondents were surveyed on the internet (response rate=1.75%; 10,304/590,000). Nearly all (n=9803, 95.30%) participants were concerned about “confirmed cases” of COVID-19, and 87.70% (n=9036) received information about the outbreak through social media websites. There were significant differences in participants’ concerns by sex (P=.02), age (P