TAIPEI • Taiwan President Tsai Ing-wen vowed yesterday to boost national security, saying her government would not submit to Chinese suppression as Beijing ramps up pressure to assert its sovereignty over the self-ruled island.

Ms Tsai's remarks came weeks ahead of island-wide local elections late next month that are seen as a bellwether for her ruling party's performance in presidential elections due in 2020.

"At this time, China's intimidation and diplomatic pressure not only hurts relations between both sides, but seriously also challenges the peaceful stability in the Taiwan Strait," she said in a National Day speech.

Taiwan will raise its defence budget every year to ensure it can defend its sovereignty, she said, by upgrading military capabilities and self-sufficiency, including resuming development of advanced training aircraft and submarines.

China, which views Taiwan as a wayward province, has increased military and diplomatic pressure on Taipei, leading to a difficult period for the President and her independence-leaning Democratic Progressive Party.

Three former allies - El Salvador, Burkina Faso and Dominican Republic - switched allegiances to Beijing this year, and the Chinese military has stepped up encirclement drills around Taiwan, which Taipei has denounced as intimidation.

Taiwan must work with others to build a coalition to defend democracy, Ms Tsai said, thanking the European Parliament and the United States for their support. Last month, the US State Department approved the sale to Taiwan of spare parts for F-16 fighter planes and other military aircraft worth up to US$330 million (S$455.4 million), a move China has said jeopardises Sino-US cooperation.

China has never renounced the use of force to bring Taiwan under its control and regularly calls the island its most sensitive issue in its ties with the US.

Relations with Beijing have nosedived since Ms Tsai came into office in 2016, with China suspecting that she wants to push for formal independence, a red line for Beijing.

On her part, Ms Tsai has repeatedly emphasised maintaining the status quo since coming to power. "I would like to pledge to everyone that we will not rashly increase antagonism, but we won't submit or yield," she said.