The transient reflectivity of gallium films induced by 150 fs laser pulses has been studied by the pump-probe technique at the pump intensities of 10(9)-10(12) W/cm(2). The time-resolved reflectivity rise of the femtosecond probe in the first 1-4 ps after the pump pulse excitation depends strongly on the pump pulse intensity. We demonstrate that the transient electron-phonon collision rate extracted from the reflectivity data is a strong function of the temperature, and thus the laser intensity. This collision rate is drastically different from that observed under equilibrium conditions. The scenario for the microscopic kinetics of the phase transition on the femtosecond time scale is discussed, and new experiments for observation of time-resolved optical properties are proposed. (C) 2002 Elsevier Science B.V. All rights reserved.