Taiwanese President Tsai Ing-wen vowed Saturday to maintain peace and stability across the Taiwan Strait in the face of increased military pressure from China, saying that "war is not an option".

Under Tsai's two terms as president, the self-ruled island has seen stepped-up warplanes and sea incursions from China -- which claims Taiwan as its territory to be claimed one day, by force if necessary.

Tsai -- who rejects that Taiwan is a part of China -- said that during her tenure, residents have shown the world "Taiwan's determination to defend itself".

"In the face of China's civil attacks and military threats, the people of Taiwan are calm and not aggressive, rational and not provocative," she said Saturday, the final day of her seventh year in office.

"War is not an option, and neither party can unilaterally change the status quo in a non-peaceful manner," she said.

Her speech comes as Taiwan gears up for its next presidential election, to be held on January 2024.

Due to the democratic island's term limits, 66-year-old Tsai will not be standing for election.

Vice President William Lai has been chosen as the presidential candidate for the ruling Democratic Progressive Party.

He has been far more outspoken about independence than Tsai, saying in January that he considers Taiwan to already be a "sovereign country".

He will be facing off with the popular mayor of New Taipei City, Hou Yu-ih.

The 65-year-old former police chief was announced as the candidate for Taiwan's main opposition party Kuomintang (KMT) -- which traditionally favours warmer ties with China.

Beijing has said any move by Taiwan towards a formal declaration of independence would prompt a military response.