This paper focuses on real-time motion planning in a dynamic environment. Most of the global existing approaches cannot satisfy real-time due to heavy computation, while local methods don't guarantee reaching the goal. In this paper we present a novel global approach based on the non-linear velocity obstacle concept. We use the rich information on the velocities admissible for the robot to build a complete autonomous navigation module, composed of a local obstacle-avoidance system coupled with an incremental global motion planner. Real-time computation issues are discussed. Results obtained in simulation for dynamic environments are presented.