Volunteers and subway workers conduct a first-aid drill at a subway station in Hangzhou, Zhejiang province. [Photo provided to China Daily]

First encounter

Xia Zhenhui, a 24-year-old employee of a local property management company and a marathon runner, said he first approached the local Red Cross Society in early 2019.

"I often took part in marathons in college and heard stories about runners collapsing and losing their lives due to a heart attack," he said.

"The stories prompted me to think about what I could do if my family members or friends suffered such an incident."

Xia completed the required training, and received a certificate in March 2019.

"Six months later, on a September afternoon, my phone began beeping and I saw a message saying that a person 615 meters from me required help as he was unconscious and not breathing," he said. "I froze for a brief moment. The app for us volunteers had gone online less than a month before and I had only registered recently. But I very quickly collected myself because I knew time was vital at that moment."

When someone is unconscious and not breathing, permanent brain damage begins after four minutes without oxygen, and death can occur about four to six minutes after that, medical experts said.