Five years ago, each classroom at her middle school in downtown Taipei had 28 students, but now it is 20, and the trend shows no sign of abating. She is thinking about starting a business, just to stay secure financially.

"My colleagues and I are definitely very concerned," 37-year-old Shen said. "Some have already had to leave for other schools."

Taiwan, with a population of 23 million, now has the dubious distinction of having the lowest birth rate in the world, according to the Population Reference Bureau, a think tank based in Washington D.C..

Taiwan's interior ministry says just 1.05 children are born per woman, down from 7.04 in 1951 and 2.10 as late as 1984.

"It's not just the lowest level ever in Taiwan, it's the lowest level in history. Nobody has ever gone that low," said Carl Haub, a demographer at the Washington bureau.

The development is a paradox in a society that remains devoted to Chinese tradition, where offspring are considered a blessing and a guarantee that the lineage will continue into the future.

Part of the explanation is economic and reflects the way a child has changed from being an asset in the rural society of half a century ago - an extra pair of hands at the family farm - to a major financial burden.

Rising prices of everything from healthcare to education have made many Taiwanese think twice before they have another child.

"There's also an unmeasurable part of it, and no one can quantify this. Young people don't come out of school with the idea that they want to raise a family," said Haub.

"There's a reaction among young women, who see how many children their mothers had, and watched them spend all that time looking after household matters, and that's not necessarily what they want to do."

Weakening family ties consolidate this mindset, as young people migrate from the countryside into the cities, away from the the watchful eyes of their parents and grandparents.

This relieves them from pressure from the older generation to produce children, and many instead opt for a materially comfortable single existence.

They are encouraged by modern media that hail the ideal of individual fulfillment, a far cry from the family-oriented tradition, experts said.

The consequences will be felt sooner than many expect, and it will be only a few years before Taiwan starts changing profoundly, they warned.

In October, the education ministry said that more than one in three of Taiwan's 164 colleges are likely to be forced to close by 2021 due to a shortage of students.

Much more serious, the island will eventually not have enough people in the labour force to support a growing number of elderly.

Current forecasts are that in 2051, more than one in three Taiwanese will be 65 years or older, up from one in 10 now.

Importing labour from mainland China on a massive scale would seem a solution, given the linguistic and cultural similarities, but it is not politically feasible, analysts warned.

Perhaps a majority of people in Taiwan are concerned about being devoured by a rapidly growing Chinese giant, and letting large armies of workers on to the island would do nothing to reassure them.

This means that if Taiwan wants to maintain its population, it has to increase its fertility rate, analysts say.

"The government has to take action now," said Haub.

However, so far the government has shown little inclination to introduce effective measures, according to Chen Yu-hua, a demographer at National Taiwan University.

"It seems the Taiwan government does not have any strong political will to do anything about it. It doesn't provide any incentive for the people," she said.

There is also no particular pressure yet from public opinion to act, as the general understanding of the issues remains low, according to Chen.

With a population density ranked as 15th in the world, many Taiwanese would welcome a drop in numbers, but the key issue is how to achieve this, she said.