NA61/SHINE is a fixed target experiment at the CERN Super Proton-Synchrotron. The main goals of the experiment are to discover the critical point of strongly interacting matter and to study the properties of the onset of deconfinement. In order to reach these goals, a study of hadron production properties is performed in nucleus-nucleus, proton-proton and proton-nucleus interactions as a function of collision energy and size of the colliding nuclei. One of the predicted signatures of the onset of deconfinement are substantial changes in dynamics of strangeness production. In this talk, I will give an overview of statistical and dynamical models of strangeness production in the vicinity of phase transition. Predictions of the models will be compared with available results on heavy-ions collisions, including new results on intermediate mass systems from NA61/SHINE.