Phase separated state of thin films of (Pr0.6Ca0.4)MnO3 on LaAlO3 and SrTiO3 substrates was investigated by means of the ultrafast time-resolved magnetooptics in the magnetic field up to 1.1 T. The photoinduced Kerr rotation and ellipticity show remarkably different magnetic-field dependence. From comparison with the static Kerr rotation and ellipticity we conclude that two different magnetic phases are present in the samples at low temperatures. According to small angle neutron scattering results one of the phases originates from nanoscopic ferromagnetic metallic clusters. Temporal dependence of the photoinduced Kerr signals indicates that upon photoexcitation changes of the volume fraction of these phases take place on a timescale of a few tens of picoseconds.