SummaryTransforming a dynamical system by adding auxiliary dynamics is one of the most recent tools to design an observer. Dynamical systems that have the properties of admitting such transformation have been widely studied. Indeed, in the existing literature, several different types of geometrical and analytical characterizations of such dynamical systems have been established. However, one finds only a few examples on this topic. Therefore, the main focus of this paper is to characterize a class of single‐output dynamical systems that can be transformed by means of a change of coordinates into an extended nonlinear observer normal form. Furthermore, this class provides examples of systems that can be transformed adding to them more than one auxiliary dynamics. To our knowledge, examples on this last fact lack in the existing research literature on this topic. Copyright © 2013 John Wiley & Sons, Ltd.