China's national college entrance exam, the gaokao, is no longer just a test that affects students and their families - it is helping to create booming markets.

Ahead of this year's exam, on Friday and Saturday, hotels near test sites are fully booked, restaurants are offering free drinks and healthy "brain food", online stores are selling out of lucky charms, and parents are swarming to temples to pray - and in many cases make donations - for their children to score high marks.

A student and her mother pray for good luck in the coming gaokao, or college entrance exam, at the Confucian Temple in Fuzhou, Fujian province, on Thursday. LIU TAO / FOR CHINA DAILY

Observers have dubbed the effect "the gaokao economy".

More than 9 million students will take the make-or-break exam this year, more than the population of Sweden. That means millions of anxious parents, who traditionally have never been shy in spending money if they think it will improve the chances of their child doing well.

To avoid wasting valuable study time commuting to and from an exam hall, for example, many families attempt to stay close by, which is good news for hotels and guesthouses.

A search for "gaokao hotels" on Ctrip's online booking service showed not one room near any test site in Beijing is vacant this weekend. Media reports in Shanghai also said some parents are paying as much as 5,000 yuan ($815) a night for five-star hotels.

Businesses are even adopting marketing strategies that target gaokao parents, with hotels promising a "home away from home", while restaurants promote healthy meals to keep youngsters focused.

Beijing eatery Hong Zhuang Yuan, whose name translates as "top-scoring scholar", has been serving "gaokao meals" for years and this year is offering students free mung bean soup.

Health products that promise to boost energy are also selling well in Shanghai. "It's the same every year," said a cashier at a drugstore near the city's Huaihai Road. "During peak times we can sell dozens of bottles of fish oil."