China claims self-ruled Taiwan as its territory, and has in the past year stepped up military and political pressure, ramping up the number of warplane incursions around the island while diplomatically isolating it.

Taiwan has increased defence spending -- allotting a record $19 billion for 2024 -- to acquire military equipment, particularly from its key ally the United States, but its quest to obtain a submarine has faced obstacles.

President Tsai Ing-wen -- strongly opposed by Beijing for her refusal to accept China's authority over the island -- launched a submarine programme in 2016 with the aim of delivering a fleet of eight vessels.

The first prototype is named "Hai Kun", which means "mythical sea creature" in Chinese, and was unveiled Thursday at a ceremony in the southern port city of Kaohsiung.

"History will forever remember this day," declared Tsai, standing in front of the vessel draped in Taiwan's flag colours.

"In the past, building submarines domestically was considered 'Mission Impossible'. But today, a submarine designed and built by our own people is right in front of everyone -- we did it," she said.

Hai Kun measures 80 metres in length and has a displacement weight of about 2,500 to 3,000 tons, and has combat systems and torpedoes sourced from the US defence company Lockheed Martin.

It will now undergo sea trials, with Tsai saying Hai Kun would be operational by 2025 -- though some defence analysts say it could take longer.

Taiwan's navy currently has two working submarines -- Swordfish-class vessels bought from the Netherlands in the 1980s.

Washington initially approved an offer in 2001 to supply eight conventional submarines, but the sale never materialised.

Over the same period, China has built itself one of the world's largest navies, with nuclear-powered submarines and aircraft carriers.

- 'Crucial element' -

China has about 60 submarines, according to the US Department of Defense, six of which are nuclear-powered and armed with ballistic missiles.

While this puts Taiwan at a clear disadvantage in terms of numbers, deploying its submarines at two major choke points -- the Bashi Channel and the Miyako Strait -- would be enough to cause problems for China, said Sifu Ou at Taiwan's Institute for National Defense and Security Research.

"They cannot sail through easily -- it is very important for Taiwan's defence."

Ben Lewis, a US-based independent expert on the Chinese military's movements around Taiwan, said the submarine will pose a risk to China's amphibious assault and troop transport capabilities.

"They have practised extensively the use of civilian vessels to augment their existing troop delivery platforms, and a submarine could wreak havoc on vessels not designed for naval warfare."

But Zivon Wang, a military analyst at Taipei-based think tank the Chinese Council of Advanced Policy Studies, said there is still a long way to go before it is "combat capable".

"The launch... does not mean that Taiwan will become very powerful right away but it is a crucial element of Taiwan's defence strategy and a part of our efforts to build deterrence capabilities."

China's state-run Global Times on Monday published an op-ed saying Taiwan's submarine deployment plan to block the PLA was "daydreaming".

"The plan is just an illusion of the island attempting to resist reunification by force," it said.