Surface signatures associated with non-linear internal waves are often seen in satellite images of the western South China Sea (SCS) slope and shelf. Observation in the deep sea, to the east, are rare. Here we report on the evolution of an energetic packet as it propagated through the deep central basin of the SCS, toward the western slope and shelf. The waves have amplitudes estimated at 170 m, half widths of 3 km, and phase speeds of 2.9 ± 0.1 m/s, faster than the mode-1 linear phase speed of 2.6 m/s. The shape and observed phase speed were consistent with the Korteweg-deVries (KdV) model over the 65-km path that they were tracked. The intrinsic velocity shear of the waves is small compared to pre-existing shears, and the waves exhibit weak turbulence. The KdV fit and a satellite-derived estimate of horizontal wave extent imply a westward energy flux of 4.5 GW for each crest.