China complains about Japanese official visiting Taiwan as Taipei pushed for cooperation

China has lodged a diplomatic complaint with Japan regarding the visit by a high-ranking official of Japan's ruling Liberal Democratic Party (LDP) to Taiwan, the Chinese foreign ministry said on Monday, as ties between the East Asian nations strain.

"China is firmly opposed and has lodged solemn representations with the Japanese side," spokesperson Lin Jian said, urging Japan to "reflect deeply on its mistake".

Taiwan President Lai Ching-te received the LDP's executive acting secretary general Koichi Hagiuda in the presidential office in Taipei on Monday, and urged closer cooperation between Taipei and Tokyo to help maintain regional stability and advance a "free and open Indo-Pacific".

Lai said he hoped the two sides would "join hands, stay united and support each other" to deepen cooperation in areas including national strategy, regional partnerships, economic security and high-tech industries.

He urged democracies to "stand together so as not to be picked off one by one."

Hagiuda's visit comes with diplomatic ties between Tokyo and Beijing at their lowest in years after Japanese Prime Minister Sanae Takaichi suggested last month a hypothetical Chinese attack on Taiwan could trigger a military response from Tokyo.

China responded vehemently and has been pushing for the Japanese leader to retract her statement.