He says, for China Rh Union, after collecting information from the patients, their information is released in the QQ groups and normally there will be volunteers offering to help in two or three days.

Xiao Yanhong, a Rh negative A blood type from Shanghai's Jinshan district who joined the union in 2011, says Xie would put aside his work to accompany her to donate blood.

"He coordinates everything and pays the cost. He is the one who has invested the most time and energy in our union," Xiao says.

Xie says he can give the donors only comfort and support. "We don't get paid, nor have any safety guarantee. The only bond between us is trust."

Xie has not calculated how many patients they have assisted over the years, but more than 10 patients have accepted their blood over the past three months.

The latest case was a 14-year-old leukemia patient from Fujian province. Xie Jianchun, the boy's father, says he posted a message on the website of China Rh Union and received a call from Xie Yingfeng the next day.

Leukemia patients need blood transfusions regularly as chemotherapy also kills red blood cells while it eliminates excessive white blood cells.

The father said his son needs a blood transfusion twice a month. But adult men in China are allowed to only donate a maximum of 400 milliliters of blood once every six months to ensure the donor's health.

"The volunteers take turns to donate blood for my son. We are really lucky to have met these good-hearted people," the father says.

But it was the failed attempt to help a girl with leukemia that left Xie Yingfeng with the deepest impression. The girl, 7, passed away before a donor could come to her help.

"I cried, mourned and sat before the computer screen for a whole day, doing nothing and not listening to anybody," he recalls.

But such dramatic emotional roller coaster is rare.

"At first I donated blood out of a kind of heroism, but now I have become more rational, or you can also call it numb. The truth is that we can't always provide help in time, or endlessly help them. It is good enough as long as we've tried our best," he says.

The official Shanghai Blood Administration Office also has a team of volunteers with rare blood types, about 20 to 30 in each district, to meet the emergency need for rare blood, according to an official from the office.

People's willingness to donate blood has been low in China in recent years, says the official. The blood donation rate in Shanghai is 1.26 percent of the population, just slightly above the 1 percent minimum target set by the World Health Organization.

Last July, China's Ministry of Health made a regulation that lifted the ban on lesbian blood donation and increased the maximum age for donors by five years to 60.