Chinese President Xi Jinping’s state visit to Seoul, which came before any meeting with North Korean leader Kim Jong-un, highlights the shift of Beijing’s strategic focus to partnership with South Korea.

During their summit talks Thursday, the fifth since they took office early last year, President Park Geun-hye and Xi discussed regional security issues, including North Korea’s nuclear program and Japan’s move to strengthen its military role, and agreed on a set of measures to elevate the Seoul-Beijing bilateral partnership to a new height.

Xi’s two-day visit, which continues through Friday and on which he is joined by a massive entourage comprised of all his key aides and about 200 business leaders as well as his wife, is a reminder of the opportunities and challenges for South Korea in deepening its relations with China.

In an article published by the People’s Daily a day before Xi arrived in Seoul, the Chinese ambassador to Seoul noted that, in the context of geopolitics in Asia, South Korea and China shared a “common destiny.”

The strengthening ties between Seoul and Being have estranged Japan and North Korea, which are moving to improve their relations. Tokyo plans to lift part of the sanctions it has unilaterally imposed on North Korea in return for Pyongyang’s cooperation in reinvestigating the abduction of Japanese citizens.

Tokyo’s attempts at expanding its military role by reinterpreting its war-renouncing constitution and glossing over its pre-1945 wartime atrocities have facilitated a joint response by Seoul and Beijing. In an apparent show of its displeasure with Xi’s visit to Seoul, North Korea has made a series of missile and rocket launches in recent days, moves that have drawn little attention from China.

Beijing’s strategic shift to Seoul appears to be part of its wider geopolitical plan to establish a regional sphere of influence to counter that of the U.S. This approach will make it increasingly difficult for Seoul officials to strike a delicate balance between the two superpowers.

The typical South Korean stance is that it will maintain a close security alliance with the U.S. while boosting the comprehensive partnership with China. But Beijing’s growing assertiveness may be forcing a choice on Seoul, which would be hard to circumvent with diplomatic rhetoric.

Some U.S. experts have said Washington has no concerns about closer ties between Seoul and Beijing, as this would help with resolving the North Korean nuclear issue. But in a move with more significant implications, the chairman of the U.S. Joint Chiefs of Staff invited his South Korean and Japanese counterparts to a meeting in Hawaii a day before Xi’s arrival in Seoul to discuss military coordination against North Korea’s nuclear and missile threats.

South Korea’s cooperation with China in coping with Japan’s revisionist course of action will be inevitably limited by the need to maintain trilateral security cooperation with the U.S. and Japan. Seoul also needs Washington to act as a regional balancer to prevent a possible military conflict between China and Japan, something which could also endanger its security.

In this context, Xi’s visit to Seoul raises, in a fundamental way, the question of whether South Korea will be able to work out and implement more sophisticated and proactive strategies to strike a delicate balance between China and the U.S.