China regards Taiwan as its sacred territory and regularly calls it the most sensitive and important issue in ties with the United States. It always complains about transit stops by Taiwan leaders in the United States, Reuters.com reported.
Tsai said she will transit Hawaii on her way home from an eight-day visit to Palau, Nauru and the Marshall Islands, which began on Thursday.
Chinese foreign ministry spokesman Geng Shuang said China had lodged “stern representations” over Tsai’s planned stopover in the United States.
China urged the United States not to send “Taiwan independence forces any wrong signal”, he added.
China views Taiwan as merely a wayward province, with no right to state-to-state relations.
The United States, like most other countries, has no formal diplomatic relations with Taiwan but is the island’s largest weapons supplier and most powerful international backer.
China and the United States are trying to end a bitter trade war and they also have differences over Chinese activity in the disputed South China Sea, as well as over human rights.
Tsai’s tour comes amid heightened tension between Taipei and Beijing, which has stepped up diplomatic and military pressure to assert its sovereignty over self-governed Taiwan.
Taipei is battling to prevent its remaining 17 allies from switching allegiance to China.
Tsai said in a statement before setting off on the tour that it was her duty to promote Taiwan internationally.
Last year, China persuaded the Dominican Republic, Burkina Faso and El Salvador to forge relations with Beijing in what Tsai called “increasingly out of control” behavior.
Chinese President Xi Jinping said in January Beijing reserved the right to use force to bring Taiwan under its control but will strive to achieve peaceful “reunification”, though democratic Taiwan has shown no interest in being run by Beijing.