The danger stems from where the bed of the South China Sea ducks under the Manila Trench, a boundary in the notoriously seismic Philippine Sea plate of the Earth's crust.

An earthquake on the Manila Trench could cause giant waves that would radiate across the shallow sea, placing major cities in harm's way, according to computer simulations by scientists in China, the United States and Japan.

According to their calculations, a 7.5-magnitude quake occurring on parts of the Trench southwest of the Philippines would unleash a wave of over two metres (6.5 feet), which would endanger a 400-kilometre (250-mile) swathe of the coast of Guangdong province, from Macau and Hong Kong in the south to Shantou in the north.

The risk of this happening over the next century is 10.12 percent for Hong Kong and Macau and 13.34 percent for Shantou, scientists believe.

 Source : Yahoo News