China Ministry of Foreign Affairs, Geng Shuang stated on April 25th 2017:
"China strongly urges the United States and South Korea to stop actions that worsen regional tensions and harm China's strategic security interests and cancel the deployment of the THAAD system and withdraw the equipment," Chinese foreign ministry spokesman Geng Shuang told a briefing.
"China will resolutely take necessary steps to defend its interests," Mr. Geng said, without elaborating.
It is a missile defense system to be in the defense of South Korea against North Korean missiles, why would China react so strongly against it?
What are those strategic security interests that may be harmed by installing that shield?