Donghai Island is an island in the southeast part of the urban area of Zhanjiang, Guangdong, People's Republic of China. It is part of Mazhang District. It has a coastline of 159.48km, with a total area of 286sqkm, making it the largest island in Guangdong and the fifth-largest island in China. In 2008, it had a population of around 160,000.