Taiwan's pool of conscripts in 2022 will be the smallest in a decade, as the island faces a demographic crisis due to its plummeting birth rate.

According to government estimates, the conscripts will total no more than 118,000. That number is set to decline further, even as the island faces Beijing's mounting aggression.

There will be a "sharp drop" in the number of males who will turn 18 - the enlistment age - in the next few years, the Legislative Yuan warned in a report in October, as it called on the defence ministry to tackle the issue as soon as possible.

Taiwan's estimated fertility rate of just over one child (1.08) per woman in 2022 is the lowest in the world, based on the CIA World Factbook. It is just below South Korea's (1.1) and Singapore's (1.16). Last year, the island with a population of 23 million saw a record low of 153,820 registered births.

While all Taiwanese males are required to undergo four months of basic military training after they turn 18, the military largely relies on voluntary enlistment for its 180,000-strong active duty cohort.

"A military of this size can defend Taiwan for now, but given the increased threats (from China) and the decrease in population, we must prepare (to do more) earlier," Dr Su Tzu-yun, from the government-funded Institute for National Defence and Security Research (INDSR) in Taipei, told The Straits Times.

Taiwan faces constant threat of an invasion by China, which claims sovereignty over the territory that it insists must be "unified" with the mainland one day.

That threat has ramped up considerably in the wake of US House Speaker Nancy Pelosi's visit to Taipei in August, which Beijing condemned as an infringement of its sovereignty and territorial integrity.

It demonstrated its displeasure with unprecedented military drills around Taiwan - including flying ballistic missiles over the island. Chinese warships and warplanes have also continued to cross the Taiwan Strait separating China and Taiwan almost daily.

Dr Yeh Yao-yuan, director of the Taiwan and East Asia Studies Program at the University of St Thomas in the United States, noted that the island's military personnel levels faced challenges beyond a declining population.

"I don't think the pay and benefits are sufficient to recruit young talents," he said, adding that for a long time, soldiers have not been viewed in high regard.

The starting salary for an entry-level soldier is US$1,235 ($1,771) per month, about 18 per cent less than the island's average salary of US$1,500, according to a Time report dated March.

Still, the increased Chinese aggression has led to calls in Taiwan to strengthen its military, including, for a start, having longer training programmes for servicemen.

According to a March poll by the Taiwanese Public Opinion Foundation, around 76 per cent of respondents aged 20 and older believed mandatory military service should be lengthened to one year.

That may become reality soon. Last week, Defence Minister Chiu Kuo-cheng said that an announcement on extending the military conscription requirement would be made by the end of 2022.

"Insufficient manpower in the military is one of the reasons for extending military service... Four months of service is not enough as threats from the enemy are now severe," he told lawmakers.

Previously, the military service requirement was two years, but the term was gradually reduced until it reached the four-month period in 2013. Servicemen are discharged as reservists, after which they undergo at least four refresher training courses, lasting between seven and 14 days, over an eight-year period.

While there is no quick solution to Taiwan's military personnel challenges, one analyst proposed a technological workaround.

"Automatic, robotic, and unmanned technologies should be further developed," said Dr Sheu Jyh-shyang, another military expert at INDSR.

"Unmanned aerial vehicles have already proven their effectiveness in Ukraine and other conflicts... similar technologies should receive high priority to support the Taiwanese military's limited human resources," he added.

Taipei anticipates that Beijing will increase its coercion and intimidation towards the island once President Xi Jinping assumes a widely expected third term in office at the Communist Party of China's congress that starts on Sunday.

While Taiwanese President Tsai Ing-wen has promised to bolster the island's defences, she has also called on the Taiwanese to do their part.

"Protecting our territory and safeguarding our nation has never been the work of the military alone," Ms Tsai said.