The plan was put together as "the security situation surrounding our nation grows severe" and with an "emergency" in mind, the government's crisis management office said.

Exactly what that emergency might be was left unspecified in the plan but it envisages the evacuation of around 120,000 people in five Japanese islets close to Taiwan.

China claims Taiwan as part of its territory and has stepped up military pressure in recent years, including near-daily air incursions. It has not ruled out using force to bring the self-ruled island under its control.

Under the plan, military vessels, private ferries and aeroplanes will be mobilised to help transport people out of the islets, including to Kyushu island at the southwestern end of the Japanese archipelago.

This amounts to more than double the usual transportation capacity, making the migration complete in the span of six days, the plan said.

The Pentagon's congressionally mandated annual report said in December that China "amplified" its diplomatic, political and military pressure against Taiwan in 2023.

Citing data from Taiwan's Ministry of National Defense, the Pentagon also reported an increase in Chinese planes crossing the Taiwan Strait centreline in 2023.