An experiment of an air shower array, a hadron calorimeter and an emulsion chamber is under way at Mt. Chacaltaya (5,200 m). Analysis of a halo event, detected by hybrid detectors, is presented. The data available for the event are on the halo (Ehalo = 750 TeV), on the height of the interaction, the energy of the electron/photon and hadronic components from the emulsion chamber, on low energy hadrons from the hadron calorimeter, and on the characteristics of the accompanied air shower (Ne = 7.0 × 107, s = 0.59) using the air shower array. The structure and origin of the event is discussed based on the observed data of various components obtained by the hybrid detectors. The event is compared to simulated events, which support the conclusion that nuclear interactions change their characteristics in the high energy region resulting in a stronger energy subdivision.