In a now-removed post on X, the Chinese consul general in Osaka Xue Jian threatened Saturday to "cut off that dirty neck without a second of hesitation".

"Are you ready for that?," he wrote, without naming Prime Minister Sanae Takaichi but quoting a news article about her remarks in parliament on Friday.

Takaichi had said armed attacks on Taiwan could warrant Japan sending troops to the island's defence under "collective self-defence".

If an emergency in Taiwan entails "battleships and the use of force, then that could constitute a situation threatening the survival (of Japan), any way you slice it," Takaichi told parliament.

"The so-called Taiwan contingency has become so serious that we have to anticipate the worst-case scenario," Takaichi, long seen as a China hawk, added.

Beijing insists Taiwan is part of its territory and has not ruled out the use of force to seize control of the self-governing island.

The Chinese diplomat's post was "extremely inappropriate", top Japanese government spokesman Minoru Kihara said Monday.

"We strongly protested and urged that it be taken down immediately," he said, adding he was "aware of multiple other inappropriate remarks" by the diplomat.

Takaichi, for her part, told parliament Monday she had no intention of retracting her statement and insisted it was consistent with Tokyo's previous stance.

But, the prime minister added she would in future refrain from referring explicitly to specific scenarios.

Security legislation passed in 2015 allows Japan to exercise the right to collective self-defence under certain conditions including if there was a clear danger to Japan's survival.

Asked about the consul's post, the Chinese foreign ministry said Taiwan was an "inseparable part of China's territory".

"China strongly urges Japan to reflect on its historical culpability on the Taiwan issue ... and stop sending any wrong signals to Taiwan independence separatist forces," ministry spokesman Lin Jian said at a regular media briefing.