The Taiwan Travel Act signed on Friday by US President Donald Trump has "dealt a serious blow" to the complex ties between China and the United States, as well as to cross-Straits peace and stability, a Chinese official said on Sunday.

The act sends the wrong signal to "Taiwan independence" separatists, said An Fengshan, spokesman for the State Council Taiwan Affairs Office.

Trump pledged shortly after taking office to support the one-China policy. The act says that the US government should encourage visits between officials of Taiwan and the United States at all levels.

"Once again, I would like to solemnly urge Taiwan that relying on foreigners to build you up will only backfire," An said.

On Saturday, the Foreign Ministry and Ministry of National Defense also spoke out.

Foreign Ministry spokesman Lu Kang said Beijing firmly opposes Trump's signing of the act and has lodged serious representations to the US side.

"As has been pointed out many times by China, the key clauses of the act, though not legally binding, severely violate the one-China principle and the three joint communiques between China and the United States," Lu said.

Beijing urges Washington to correct its mistake, stop pursuing any official ties with Taiwan or improving its current relations with Taiwan in any substantive way, Lu said.

Taiwan-related issues should be handled properly and cautiously, Lu said.

Wu Qian, spokesman for the Defense Ministry, warned in a statement issued later on Saturday that the act interferes in China's domestic affairs and undermines the development of ties between China and the US, including their militaries.

Taiwan is a part of China, and matters regarding it are strictly internal affairs, Wu said.

To avoid inflicting serious damage on China-US relations, as well as on peace and stability, Wu said, the US should keep its promises, rectify its wrongs, refrain from implementing certain clauses of the act, stop making military contacts and stop selling arms to Taiwan.

Yuan Zheng, a senior researcher on US foreign policy at the Chinese Academy of Social Sciences, said the act will motivate the separatists in Taiwan and worsen the situation there.