Participants await the start of the Hefei event on Oct 25, 2015. [Zhu Lixin/China Daily]

An amateur marathon runner collapsed and later died in Anhui province on Sunday, highlighting the danger of competing in such races without proper preparation.

The Hefei International Marathon and Chinese National Marathon Championship in Binhu New District attracted more than 20,000 runners from around the country. Among them many amateurs were taking part in the 21.0975 kilometer half-marathon.

Two-and-a-half hours after the 8am start, leading amateurs were beginning to cross the finish line. One collapsed suddenly at the 21-km mark and medical staff found Li Li (not his real name) unconsciousness having suffered a cardiac arrest. The 30-year-old was sent by ambulance to Binhu Hospital but at about 2pm was pronounced dead.

Li Li's pregnant wife and mother-in-law were heartbroken, while other relatives and colleagues also shed tears. Li worked as a security guard in Hefei for an airline company.

According to Yangcheng Evening News in Guangzhou, among the 800-plus full marathon events around the world each year, the probability of suffering sudden death while running a marathon is about one in every 50,000. Last year there were at least four reported cases of sudden death during such races on the Chinese mainland.

On March 30, 2014, a woman suffered a heart attack, collapsed and later died during the China Zheng-kai International Marathon in Henan province.

On June 25, freshman Qiu Feng suffered a heart attack after running 16-km during the Kunming Marathon in Yunnan province and died an hour later.