China has expressed "serious concerns" to Washington and Seoul after key components of an advanced US anti-missile system were installed in the Republic of Korea, Foreign Ministry spokesman Geng Shuang said on Wednesday.

"We strongly urge the United States and ROK to cancel the deployment of the Terminal High Altitude Area Defense anti-missile system, and withdraw related equipment," he said, asking the two countries to stop actions that intensify regional tensions and damage China's strategic security interests.

"China will resolutely take necessary measures to defend our own interests," he added.

The ROK Defense Ministry on Wednesday confirmed media reports that part of the THAAD system were deployed to a site in the country's southeastern region.

"China pays a great deal of interest to related reports, and we have expressed solemn concerns to the US and ROK," Geng told a daily press conference in Beijing.

According to Geng, the deployment of THAAD will upset the regional strategic balance and further provoke tensions on the Korean Peninsula.

"It does not help to realize the goal of denuclearization on the peninsula as well as regional peace and stability. It goes against the efforts of solving the issue through dialogue and negotiations, and severely damages China's strategic security interests," he said.