In 1981, when mainland China's first international marathon was launched in Beijing, fewer than 200 people took part. Last October, the 33rd edition of the event drew 30,000 runners from 40 countries, and all the race slots were snapped up just 13 hours after registration opened.
Two months later in December, the 18th edition of the Shanghai International Marathon saw a record 35,000 runners from more than 80 countries, with sign-ups filling to capacity within days.
Running has caught on in the mainland so rapidly in recent years that the race calendar has ballooned. In 2010, the Chinese Athletic Association (CAA) held 12 official running events; in 2012 there were 33.
This year, there will be 53 events in the annual national running series, the association revealed in January. The bulk of these races are marathons (42.195 kilometres), though there are events ranging from 10 kilometres to more than 100 kilometres.
"Adding other races nationally, the number of all running events in the mainland will exceed 100, with more than two million participants in total," says Cui Jian, general manager of eRun360.com  China's biggest online running community.
Launched in October 2012 in response to the running boom, eRun360 has more than 60,000 registered members and 1.2 million daily page views.
Active Network, a US-based company that provides online race registration services, opened offices on the mainland last year, when 10 races used its registration platform.
This year, some 40 events are set to come on board, says Jean Su, Active's director of China operations. "Our statistics show that the full and half marathon distances are the most popular. Runners are mainly between 25 and 40 years, with more men than women," says Su.
Running fever has been driven domestically, with locals accounting for most entrants at races.
The Xiamen International Marathon in January attracted a record 77,000 participants. Sixty per cent of the runners came from Xiamen, 1.5 per cent were foreigners from more than 40 countries and regions, and the rest came from other parts of the mainland.
The mainland's National Fitness Programme, which was launched in 1995, has helped boost participation in running, according to CAA chairman Duan Shijie.
"The races are not limited to professional runners. People from all walks of life and of different ages can participate, enjoying the fun of running as well as the festive atmosphere," said Duan in a Xinhua article.
Wealthy mainlanders now realise the importance of exercise. Among those driving the boom are "many corporate executives and middle-class elite who wish to stay healthy and relieve stress", says Cui.
The sport benefits not only participants, but also the hosts. Many cities are launching running races as a way to promote tourism and boost their image. Marathon routes are planned to showcase landmarks and scenery.
Shenzhen hosted its first international marathon last December, attracting 10,000 runners from 30 countries. The city's authorities were inspired to organise their own race after seeing the success of the Xiamen International Marathon, which reportedly reaps about 100 million yuan (HK$127 million) annually in tourism for the city.
The Xiamen event is one of four mainland marathons to have the "gold label" given by the International Association of Athletics Federations (IAAF. The others are the Lanzhou, Shanghai and Beijing races.
Meanwhile, interest among runners abroad is increasing. "On a daily basis, we receive inquiry to various marathons across China, not only from locals but also runners from around the world," says Troy de Haas, a sports travel agent with Flight Centre.
The Greater China office of the Australian-based travel agency sold 25 running packages to the mainland last year, up from just two in 2012, says de Haas. "This year, we expect that to grow even further to more than 50 packages," he says.
"Many of these regional areas and regional governments want to promote tourism and subsidise your race entry. For example the Jinshanling Great Wall Marathon is US$200, and includes race entry, transfers, three nights accommodation, a welcome dinner, pasta party and post-race party, compared to US$600 just for a start bib to the New York City Marathon."
De Haas, himself a top competitive runner, says foreigners are attracted to mainland races because of the exotic settings.
The Great Wall Marathon, for example, takes participants through villages and over a section of the wall in Beijing with more than 5,000 steps.
Since the first race in 1999, the field has grown steadily to more than 2,500 in 2013 with runners from more than 50 countries. It's not a fast course - last year's winners took three hours, nine minutes and 18 seconds, more than an hour off the marathon world record - but it's one you won't forget.
Along with road races, trail ultramarathons are also taking off. Hundred-kilometre races in Beijing, Shandong, Dalian, Dali, Guizhou and Hangzhou are increasingly popular, says Cui.
Tina Lewis, a Canadian elite trail runner with the Salomon International Team, won The North Face 100 kilometre race in Beijing last year. It was her first trip to China - and Asia.
"I really enjoyed the course," says Lewis, who is based in Boulder, Colorado. "It was unique and completely different than what I am used to in North America. There were a lot of steps and untravelled trails.
"The climbs were gruelling but satisfying. The scenery was spectacular - mountain views and canyons. The course brought you through little villages, which is a great way to experience the culture."
Michal Bucek, a Hong Kong-based Slovakian professional triathlete who will do the Yishan 50 kilometre Mountain Marathon again in May, says such events allow athletes to see other parts of China.
"People usually only know the big cities like Beijing or Shanghai, they don't know about the mainland countryside, which is amazingly beautiful."
Eric LaHaie, managing director at Stack Asia Pacific and a top Hong Kong-based trail runner, has raced several times in the past six years in the autonomous region of Xinjiang, in the northwest. He says the region's unique culture and geography draw him back.
"You have amazing deserts, snow-capped mountains, rivers, and more," says LaHaie, who won the 2009 Gobi March, a 250 kilometre stage race held in the Gobi Desert in Xinjiang. "The culture combined with the landscape can be unmatched at times - the air pollution is another story."
Indeed, air quality is a hot issue with running on the mainland. On the day of last year's Shanghai Marathon, the air pollution index went past 300, with the level of the most harmful pollutants exceeding more than 10 times that deemed safe by the World Health Organisation.
"I ran my first marathon today," a runner wrote on social media site Weibo. "The air was so polluted that my nose turned black after the run. It was like I just got out of a coal mine."
The race organisation also tends to lag other more established running markets.
"The quality needs to be improved," says Cui. "It's a long journey to catch up with six world marathon majors, Boston, Chicago, New York, London, Berlin and Tokyo."
At the Beijing Marathon, for example, slower runners in the second half of the field often find that the aid stations have run out of water, says Active Network's Su. Many races also lack online registration and payment - some do not have websites or information in English - which makes signing up a challenge.
Spotty organisation, last-minute changes and loose or undefined rules are not uncommon. But it all adds to the experience. "Racing in China is a bit of an adventure, which I love," says LaHaie.
If you're thinking of joining an event on the mainland, de Haas says it's best to be well prepared: bring race nutrition, medication, strapping tape, extra gear and so on.
"Take a deep breath and chill out," says de Haas. "Things will come up that will surprise you or put you outside your comfort zone. But everyone is in the same situation, so the better you can handle the situation and move on, the better you will fare in the race."
Despite the rapid increase in running events, China still has a long way to go to match that of more established running markets such as US and Japan, which had some 800 and 200 marathons respectively in 2012, says CAA's Duan.
"In the US, there are over 200 marathons for a population of 300 million, so with a population of around 1.5 billion Chinese, there is space for many more races," IAAF president Lamine Diack said in an interview at this year's Xiamen Marathon.
"The fact that the Chinese government and local civic authorities are committed to working together with the CAA to support this development is a positive sign," Diack says.
Apr 18-20: Shangri-la Lijiang Action Asia Three-day Ultra Marathon, Yunnan
Apr 20: Jinshanling Great Wall Marathon, Hebei
May 17: Dalian Marathon
May 17: The Great Wall Marathon, Beijing
Distances: 8.5 km/21km/42km
May (date TBC): The North Face 100 China, Beijing
Jun 1-7: Racing The Planet Gobi March, Xinjiang
Jun 15: Lanzhou Marathon
Oct 19: Beijing Marathon
Dec 7: Shanghai Marathon