Volunteers walk on the street in Qingdao, east China's Shandong Province, June 1, 2018. The 18th Shanghai Cooperation Organization (SCO) Summit is scheduled for June 9-10 in Qingdao. Volunteers are easily seen on the street. (Xinhua/Li Ziheng)

Volunteers give information to tourists at a service station in Qingdao, east China's Shandong Province, June 2, 2018. The 18th Shanghai Cooperation Organization (SCO) Summit is scheduled for June 9-10 in Qingdao. Volunteers are easily seen on the street. (Xinhua/Liu Junxi)

Photo shows the supplies stored at a volunteer service station at the May Fourth Square in Qingdao, east China's Shandong Province, June 3, 2018. The 18th Shanghai Cooperation Organization (SCO) Summit is scheduled for June 9-10 in Qingdao. Volunteers are easily seen on the street. (Xinhua/Sadat)

A volunteer guides the tourists near the May Fourth Square in Qingdao, east China's Shandong Province, June 2, 2018. The 18th Shanghai Cooperation Organization (SCO) Summit is scheduled for June 9-10 in Qingdao. Volunteers are easily seen on the street. (Xinhua/Liu Junxi)

Shan Zhixian (R), 77, volunteer as an interpreter at Lao She memorial house in Qingdao, east China's Shandong Province, June 1, 2018. The 18th Shanghai Cooperation Organization (SCO) Summit is scheduled for June 9-10 in Qingdao. Volunteers are easily seen on the street. (Xinhua/Zhu Zheng)

Three volunteers stand on duty in Qingdao, east China's Shandong Province, June 3, 2018. The 18th Shanghai Cooperation Organization (SCO) Summit is scheduled for June 9-10 in Qingdao. Volunteers are easily seen on the street. (Xinhua/Li Ziheng)