The subduction megathrust under the Manila Trench has been accumulating strain over a period of 440 years or more, and could be the source for a giant earthquake of M-w similar to 9. We present a plausible earthquake rupture model constructed from seismic and geodetic data, together with hydrodynamic simulations of the potential tsunami with COMCOT (COrnell Multi-grid Coupled Tsunami model). Results indicate that this megathrust poses a risk of devastating tsunami for the Philippines, Southern China, Vietnam and other population centers bordering the South China Sea. (C) 2008 Elsevier Ltd. All rights reserved.