This paper addresses the problem of observer design fora class of switched system, where the discrete state evolution is ledby a Petri net. This class may have modes in which the state is notfully observable. A new hybrid observer composed of a discrete anda switched continuous parts in interaction is proposed. The discretepart is based on Unknown Input observer to reconstruct the discretestate through the observation of measurable continuous outputs of thesystem. The switched continuous observer is based on higher ordersliding mode techniques. It gathers partial information from individualmodes to solve the continuous state estimation of the entire system.Simulation results show the effectiveness of the proposed approach