This paper presents a method based on inverse kinematics with task specification for online human to humanoid motion imitation. We particularly focus on the problem of lifting and placing feet on the floor during the motion, allowing change of support during stepping or locomotion. The approach avoids the use of motion primitives that limit the robot motions to what had been learned. A direct transposition of movements is generated, allowing the robot to move freely in space as the human model does, at a velocity close to the reference one. The approach is validated on the humanoid robot NAO and shows very promising results for the use of online motion imitation.