Following previous studies (Zhao et al., 2019, de Silva et al., 2009), we modelled the epidemic curve obeying the exponential growth. The nonlinear least square (NLS) framework is adopted for data fitting and parameter estimation. The intrinsic growth rate (γ) of the exponential growth was estimated, and the basic reproduction number could be obtained by R 0 = 1/M(−γ) with 100% susceptibility for 2019-nCoV at this early stage. The function M(∙) is the Laplace transform, i.e., the moment generating function, of the probability distribution for the serial interval (SI) of the disease (Zhao et al., 2019, Wallinga and Lipsitch, 2007), denoted by h(k) and k is the mean SI. Since the transmission chain of 2019-nCoV remains unclear, we adopted the SI information from SARS and MERS, which share a similar pathogen as 2019-nCoV. We modelled h(k) as Gamma distributions with a mean of 7.6 days and standard deviation (SD) of 3.4 days for MERS (Assiri et al., 2013), and mean of 8.4 days and SD of 3.8 days for SARS (Lipsitch et al., 2003) as well as their average, see the row heads in Table 1 for each scenario. Table 1 The summary table of the estimated basic reproduction number, R0, under different scenarios. The estimated R0 is shown as in the ‘median (95%CI)’ format. The ‘reporting rate increased’ indicates the number of fold increase in the reporting rate from January 17, when WHO released the official diagnostic protocol (World Health Organization, 2020b), to January 20, 2020. Reporting rate increased Estimated R0 Same as MERS SI 7.6 ± 3.4 SI in average 8.0 ± 3.6 Same as SARS SI 8.4 ± 3.8 (unchanged) 5.31 (3.99–6.96) 5.71 (4.24–7.54) 6.11 (4.51–8.16) 0.5-fold 4.52 (3.49–5.76) 4.82 (3.69–6.20) 5.14 (3.90–6.67) 1-fold 4.01 (3.17–5.02) 4.26 (3.34–5.38) 4.53 (3.51–5.76) 2-fold 3.38 (2.75–4.12) 3.58 (2.89–4.39) 3.77 (3.02–4.67) 4-fold 2.73 (2.31–3.22) 2.86 (2.40–3.39) 3.00 (2.50–3.58) 8-fold 2.16 (1.90–2.45) 2.24 (1.96–2.55) 2.32 (2.02–2.66) Note: ‘SI’ is serial interval. ‘MERS’ is Middle East Respiratory Syndrome, and ‘SARS’ is the Severe Acute Respiratory Syndrome.