China's first domestically manufactured aircraft carrier, shown here in Dalian, sailed through the Taiwan Strait
China's first domestically manufactured aircraft carrier, shown here in Dalian. AFP / -

The de facto US ambassador to Taiwan on Friday expressed concern that Beijing was attempting to influence the island's coming elections, days after China sent its first domestically built aircraft carrier through the Taiwan Strait.

Beijing confirmed earlier this week that the carrier traversed the strait separating China from self-ruled Taiwan, saying it was "routine" training.

"We of course regard any of these threatening actions with concern," said Brent Christensen, the director of the American Institute in Taiwan (AIT), when asked to comment on the sail-by.

AIT serves as the de facto American embassy in Taiwan.

The United States switched diplomatic recognition from Taiwan to China in 1979, but has remained an important ally -- and arms supplier -- to Taipei.

"As to the elections, of course we are aware that China is attempting to apply pressure through various means on Taiwan. Certainly these attempts to influence Taiwan's democratic process are our concerns," he added.

China's sail-by comes as Taiwan gears up for presidential elections in January, with Beijing-sceptic President Tsai Ing-wen seeking a second term against a challenger who favours warmer ties with China.

Christensen said Washington views any efforts to determine Taiwan's future by other than peaceful means as "a threat to peace and security in the Western Pacific".

Foreign minister Joseph Wu tweeted on Sunday that China "intends to intervene" in Taiwan's elections", adding: "Voters won't be intimidated"!

Taiwan's defence ministry said it had dispatched ships and planes to track and closely monitor the carrier's movements, and that US and Japanese vessels trailed it in the narrow waterway separating the island from mainland China.

Beijing has stepped up military and diplomatic pressure on Taiwan since Tsai came to power in 2016, as her government refuses to acknowledge that the self-ruled, democratic island is part of "one China".

Tsai -- who has voiced support for Hong Kong's pro-democracy movement -- has described the elections as a fight for Taiwan's freedom and democracy.

China still sees Taiwan as part of its territory awaiting reunification, by force if necessary.

China