Students leave a gaokao venue in Xingtai, Hebei province, after their first exam on Tuesday. MU YU / XINHUA

The fall in the number of students taking the gaokao will force some colleges and universities to find novel recruitment methods if they want to enroll enough students, education experts have warned.

The annual national college entrance exam began on Tuesday, with 9.4 million students taking it nationwide, 20,000 fewer than last year.

At least 13 of China's 34 municipalities, provinces and regions saw a fall in the number of students registering for the exam this year.

In Beijing, Liaoning and Jiangsu provinces, the numbers have fallen to new lows, according to an annual survey on the gaokao and enrollment released by education portal eol.cn.

The gaokao is considered the most important exam in China, as only a small proportion of the students can be enrolled at top universities each year.

Chen Zhiwen, editor-in-chief of eol.cn, said the fall in numbers is not good news for some lesser-known colleges and universities.

"Fewer students taking the gaokao mean it will be more difficult for these colleges and universities to recruit enough students," Chen said.

He believes the fall is due to the shrinking population of college-age students and more Chinese students wanting to study overseas.

The eol.cn report, citing population authorities, said 25 million people were born in China in 1990, leading to a peak in the number of gaokao takers in 2008.

After 1990, the number of newborns fell — reflected from 2009 to 2013, when gaokao takers declined for five consecutive years. The fall in numbers ended in 2014 and they have stabilized at about 9.4 million since then.

However, an increasing number of Chinese students are heading overseas to study. Last year, more than 520,000 Chinese went abroad to study — the largest number ever.

Chen believes that under such circumstances, the student recruitment issue facing some colleges and universities will continue.

Xiong Bingqi, vice-president of the 21st Century Education Research Institute, said one solution is to cultivate the characteristics and strengths of these educational institutions.