China's over three-decade-old one- child policy has resulted in the closing down of five high schools in the last four years in a county that has been proud of being a pioneer in implementating the controversial norm that has been blamed for the looming demographic crisis.

The number of high schools in Rudong county in east China's Jiangsu province has come down from nine to four in the past four years, a cruel but irreversible trend, Chen Jian, deputy head of the county's education bureau said.

"There are not enough students. Keeping all these schools open would have wasted a lot of resources," he told state-run China Daily.

Chen taught English at the Rudong Senior High School, one of the county's two best senior high schools, before becoming its principal.

"Five or six years ago, our school had a maximum of 27 classes in one grade and each class had nearly 70 students," Chen said.

The numbers were swollen by students from outside the district whose parents used every means available to enable their children to attend the school in hope they would learn how to score high marks in the gaokao, China's annual national college entrance exam and attend a top institution.

But that's all history now. This fall semester, the school's 10th grade has only 17 classes, each of which has only about 50 students, he said.

It is a sad story for a county that prides itself as a pioneer in implementation of one child policy.

Although China's family planning programme officially started in the 1970s, Rudong voluntarily introduced the policy in the 1960s.

The move resulted in a low birth rate in the 1970s, just as other parts of China were just beginning to implement the policy. Strangely Rudong now acquired a new title of being "Longevity Town" because it is home of some of the most aged people.

By the end of 2013, the county was home to 147 people aged 100 and older, 39 men and 108 women.

Chen Youhua, a professor of demographics at Nanjing University, said that only three factors can change the age structure of a region's population - birth, death, and emigration.

There's little doubt the low birth rate has played a role in Rudong's ageing process because the family planning policy prevented about 500,000 births in the past three decades, according to the county's estimates, the report said.

In defence to the one child policy, Chinese officials claim that it has prevented over 400 million births ensuring some level of prosperity. The government now allows a second child for the couples born to one child families.

The effect of the nationwide relaxation of the family planning policy, which was announced earlier this year, won't be seen in the county for some time.