Police vessels leave Sanya, south China's Hainan Province, April 17, 2017. Two Chinese maritime police vessels on Monday left Sanya for a China-Vietnam joint fishery inspection. The inspection in the Beibu Gulf involves two police vessels from each side and will be conducted over three days, ending Thursday. Joint inspections began in 2006 as an annual event, and were increased to twice a year in 2016. (Xinhua/Mao Siqian)