Zhang Juntian, deputy head of the team, said, "We cannot relax for one moment, because there is always hidden danger."

Taking only a few days off when his wife had their baby, Zhang said: "She understands and supports my work. She often says that only when everyone stays on top of their job can Ruili be truly safe."

According to experts, guarding the borders in Southwest China is key to preventing COVID-19 cases, which is vitally important nationwide and "a bottom line for security" as the nation pursues the goal of zero infections.

Ruan Chengfa, former Party secretary of Yunnan, said the province aims to plug loopholes in illegal immigration and emigration by improving infrastructure, tightening inspections and optimizing community governance.

When night falls, the 160-km border with Myanmar in Ruili is lit for patrol work, and more than 3,500 border workers on are duty in different shifts day and night. In some remote areas, the local power supply bureau has invested more than 3 million yuan ($468,300) to supply electricity.

Thousands of locals have also sacrificed their holidays and family reunions.

Li Ruizhong, an officer with the exit and entry management unit at Tengchong police station, helps foreigners worried about the pandemic, calling them in individually to reassure them and provide self-protection instruction.

When the pandemic emerged, vehicles were barred from the roads in Tengchong and the border points were closed. Li and her colleagues helped more than 800 people from Myanmar return home. She also worked overtime to track outsiders and investigate criminal cases that threatened border security.