Acoustic emission (AE) method was used to investigate the electric-field-induced-phase transition in the well-known relaxor Pb(Mg1/3Nb2/3)O-3 (PMN). We show that in the field cooling process the induced-phase transition is accompanied by an AE signal, which reflects relaxation of the strong stress, associated with arising of a macroscopic domains structure similar to martensitic phase transition. However, using a procedure in which the field is applied after a zero field cooling, no AE signal is detected even after a very long time higher than expected for the appearance of the induced-phase transition. The comparison with previous x-ray-diffraction results allowed to get in the last case interesting insights on the local and long-range polar order of the induced ferroelectric state because of absence of the relaxation of the strong stress due to percolation mechanism of this phase transition