BACKGROUND: The outbreak of coronavirus disease 2019 (COVID-19) is now becoming an enormous threat to public health. The clinical spectrum of COVID-19 is extensive, of which critical cases are with rapid disease progression and high mortality. The aim of our study is to summarize the characteristics of different subtypes and explore risk factors of illness severity for early identification and prompt treatment. METHODS: In this retrospective study, we collected data of patients confirmed COVID-19 in Zhejiang Province from 17 January to 12 February 2020. According to the definition of clinical classification, we divided confirmed cases into four types, and summarize epidemiological and clinical characteristics, laboratory and radiograph findings, treatments, and outcomes, respectively. Moreover, we used univariate and multivariate ordinal logistic regression models to explore risk factors for the severity of illness in patients with COVID-19. RESULTS: A total of 788 patients were enrolled in our study, of whom 52 cases (6.6%) were mild type, 658 cases (83.5%) were common type, 61 cases (7.2%) were severe type, and 17 cases (2.2%) were critical type. Multivariate ordinal logistic regression demonstrated increasing odds of the severity of illness in patients with COVID-19 associated with male (odds ratio [OR] = 1.7, 95% confidence interval [CI]: 1.2-2.6 P = 0.008), fever (OR = 3.6, 95% CI: 2.1-6.3, P < 0.001), cough (OR = 1.7, 95% CI: 1.0-2.9, P = 0.041), hemoptysis (OR = 3.4, 95% CI: 1.1-10.3, P = 0.032), gastrointestinal symptoms (OR = 1.9, 95% CI: 1.0-3.5, P = 0.047), hypertension (OR = 2.6, 95% CI: 1.2-5.6, P = 0.013). With the increase of age-grading, risk for the severity of illness was gradually higher (</= 18 years [OR = 1.0], 19-40 years [OR = 12.7, 95% CI: 4.5-36.0, P < 0.001], 41-65 years [OR = 14.8, 95% CI: 5.2-42.1, P < 0.001], >/= 66 years [OR = 56.5, 95% CI: 17.1-186.5, P < 0.001]). CONCLUSIONS: Clinicians should pay close attention to these features in patients with COVID-19 including older age, male, fever, cough, hemoptysis, gastrointestinal symptoms and hypertension to identify the severity of illness as early as possible.