A Chinese mainland spokeswoman on Monday urged the United States to stop any act that runs counter to the one-China policy after US President Joe Biden said the US would intervene militarily if the mainland were to "invade" Taiwan.

At a news conference in Tokyo on Monday, Biden said "yes" when asked if he was willing to get involved militarily to defend Taiwan if the mainland "invaded". However, he also said the US supports the one-China policy.

Zhu Fenglian, a spokeswoman for the Taiwan Affairs Office of the State Council, said there is only one China in the world and Taiwan is a part of China, and the Taiwan question is China's internal affair and brooks no foreign interference.

The one-China policy is the political foundation of Sino-US relations, she said.

Zhu urged the US to stop any act that runs counter to the one-China policy and the three China-US joint communiques, and cease going further down a wrong path.

"Attempting to play the 'Taiwan card' and use Taiwan to contain the mainland is like playing with fire, and those who play with fire will get burned," she said.

Zhu said Taiwan's Democratic Progressive Party has been colluding with foreign forces and seeking "independence", resulting in the current tense and turbulent situation across the Taiwan Straits.

She warned the DPP to immediately stop the act of splitting the country and seeking "independence" by relying on the US. "Otherwise, they will have no good end," she added.