China is the third largest country in the world, situated in eastern Asia on the western shore of the Pacific Ocean, with an area of 9.6 million square kilometres. China has a continental climate varying from the south which is tropical and subtropical to the frozen north. The northern part of Heilongjiang province has long winters but no summers; while Hainan Island has long summers but no winters. The Huaihe River valley is marked by distinctive seasonal changes, but it is spring all year round in the south of the Yunnan-Guizhou Plateau. China's high tundra zone is situated in Qinghai-Tibet, where the temperature is low in all four seasons.