Law-enforcement authorities from China, Laos, Myanmar and Thailand joined forces on Tuesday for the start of the 99th Mekong River joint patrol.
A total of five vessels from the four countries participated in the operation. Three Chinese vessels departed from Jingha Port, Xishuangbanna Dai Autonomous Prefecture, in southwest China's Yunnan Province.
Before the patrol, law-enforcement authorities of the four countries held a video conference to discuss the security situation of the river and reached an agreement to jointly crack down on illegal activities.
Since September this year, the officers from the four countries have solved eight illegal immigrant cases and arrested 86 suspects.
The Mekong River, known as the Lancang River in China, is a vital waterway for cross-border shipping.
China, Laos, Myanmar and Thailand have been carrying out joint patrols on the Mekong River for eight years.