Surface freezing in a liquid eutectic Ga-Bi alloy has been studied by second harmonic generation and plasma excitation in several cooling and heating cycles at different temperature rates. An ordered solid-like film is observed on top of the bulk liquid which forms at a temperature well above the eutectic temperature. The hysteresis behaviour of crystallisation and melting of this film indicates that this surface phase transition is of first order, which is reported for the first time.