Fig 1. SEIR model.

Graphical scheme representing the interactions among different stages of infection in SEIR Model. In this model, S_it, E_it, $I_{it}^T$, $I_{it}^{NT}$ and N_it denote the susceptible, exposed, detected infected, undetected infected and total population in city i and time t.${\beta }_t^{NT}$ and ${\beta }_t^T$ are the rate of transmission for undetected infected individuals and detected infected individuals, respectively. α_t is the testing rate in time t.Z_t denotes latency period through which patients switch from exposed stage to infection stage. A_it is within-city population flow in city i in time t. Spatial spread of the disease is governed by the daily number of people travelling from city j to city i in time t(M_ijt).