We compare the results of the transport and time-resolved magnetoluminescence measurements in disordered two-dimensional (2D) electron systems in GaAs-AlxGa1-xAs heterostructures in the extreme quantum limit, particularly in the vicinity of the metal-insulator transition (MIT). At filling factors nu<1, the optical signal has two components: the single-rate exponentially decaying part attributed to a uniform liquid and a power-law long-living tail specific to a microscopically inhomogeneous state of electrons. We interpret this result as a separation of the 2D electron system into liquid and localized phases, especially because the MIT occurs strikingly close to those filling factors where the liquid occupies 1/2 of the sample area (the percolation threshold condition in two-component media).