China and Japan plunged into one of their most heated diplomatic confrontations in years after Beijing summoned Japan’s ambassador over Prime Minister Sanae Takaichi’s stark warning that a Chinese military operation against Taiwan could justify Japan activating its right to collective self-defense.

The clash quickly escalated into a rare exchange of mutual summonses, sharp public rebukes and a controversial threat from a Chinese diplomat that Tokyo denounced as unacceptable.

China’s Vice Foreign Minister Sun Weidong called in Ambassador Kenji Kanasugi on Thursday and issued what Beijing described as "serious demarches,” accusing Takaichi of making "erroneous, extremely dangerous” remarks that violated the one-China principle and the political foundation of bilateral ties.

Sun said the prime minister "refused to change course” despite repeated protests and warned Japan of unspecified consequences if it continued challenging Beijing’s position on Taiwan.

Takaichi’s comments to parliament last week triggered the uproar.

She said that any Chinese attack or naval blockade of Taiwan could constitute a "survival-threatening situation,” a designation that would permit Japan to exercise collective self-defense under its 2015 security laws.

Takaichi stressed she was outlining a worst-case scenario and insisted she would not retract her remarks, which she argued were consistent with long-standing policy.

The dispute deepened after Chinese Consul General in Osaka Xue Jian posted on social media that he would "cut off that dirty neck without a second of hesitation,” in what appeared to be a direct reference to Takaichi.

Though the post was deleted, Tokyo summoned China’s ambassador, Wu Jianghao, and filed a strong protest, calling the comment "extremely inappropriate” and demanding action.

Chief Cabinet Secretary Minoru Kihara reaffirmed that Japan’s stance on Taiwan remains unchanged under the 1972 joint communique but emphasized that peace and stability in the Taiwan Strait are vital for Japan’s security and the wider region.

He urged Beijing to avoid actions that further inflame tensions.

Beijing, meanwhile, said it "will by no means tolerate” interference in its unification plans and again pressed Japan to retract the prime minister’s comments.

Takaichi told lawmakers she would refrain from publicly outlining military scenarios in the future but held firm that her earlier statement would stand.