China said it has lodged serious representations to the United States after US President Donald Trump signed a law laying the groundwork for possible naval visits between Taiwan and the United States.

The one-China policy constitutes the political foundation of China-US relations, and China is firmly opposed to any official exchanges, military contact and arms sales between Taiwan and the US, Foreign Ministry spokesman Lu Kang said on Thursday.

On Tuesday, Trump signed into law the National Defense Authorization Act for the 2018 fiscal year. It contains provisions about studying the feasibility of mutual visits between Taiwan and the US and "normalizing" the transfer of defense equipment and services to the island.

Although the Taiwan-related provisions of the law are not legally binding, they seriously violate the one-China policy and regulations of the three joint statements between China and the US, Lu said.

"It is interference in China's internal affairs," he said at a daily news conference in Beijing, urging the US to fully recognize the harmful nature of such provisions.

He called on the US to properly handle Taiwan-related issues and to avoid harming the overall cooperation between the two countries, as well as cross-Straits peace and stability.

Under the three joint statements, the US is obliged to abide by the one-China policy, recognizing that Taiwan is part of China and the Government of the People's Republic of China is the sole legal government of China.

Li Haidong, a professor of US studies at China Foreign Affairs University, said the act represents the US Congress' long-standing view on dealing with Taiwan-related issues, but it depends on Trump to decide whether to put it into practice.