This paper concerns the design of a nonlinear observer through a transformation of a nonlinear system into an observer form that supports a high gain observer. Sufficient geometrical condition is deduced to guarantee the existence of change of coordinates allowing the transformation of a nonlinear system into the proposed normal form. The result is highlighted by studying the Susceptible Exposed Infected and Recovered (SEIR) model. (C) 2013 Elsevier Ltd. All rights reserved.