In the northeastern South China Sea, fast westward moving nonlinear internal waves (NLIWs) emanate nearly daily from the Luzon Strait during spring tide. Their propagation speed of about 2.9 meters per second is faster than NLIWs previously observed in the world's oceans. The amplitudes of these waves reach 140 meters or more, and they are the largest free propagating NLIWs observed to date in the interior ocean. These NLIWs energize the top 1500 meters of the water column, moving water up and down at timescales as short as 20 minutes. While their associated energy density and energy flux are the largest observed to date, the exact source of these giant waves has yet to be determined.