Sintering and its final stage of coalescence of silver nanoparticles with various morphologies have been investigated in vacuo between 400 and 1000 K by molecular dynamics simulations using the embedded atom method (EAM). It was found that the Ag nanoparticle melting temperature increases with increasing particle size and approaches the bulk melting point of Ag for bigger particles (>10 nm) consistent with simulation literature and experimental data. The motion of surface and bulk Ag atoms within Ag nanoparticles is monitored closely during their sintering. Early on, the sintering or coalescence of nanoparticles is dominated by surface diffusion whereas a transition toward plastic flow sintering can be observed near their melting point. The sintering rate of straight nanoparticle chains is much slower than that of more compact structures. The formation of new crystal domains during Ag particle sintering is demonstrated for the first time to the best of our knowledge, and mechanisms leading to formation of polycrystalline particles are revealed.