China has made solemn representations to the US side.

中方已就此向美方提出严正交涉。

youdao

A: China took the case seriously and has made solemn representations to the DPRK side.

答：这个事件发生后，中方给予了高度重视，向朝方进行了严正交涉。

youdao

A: the Chinese Government has repeatedly made solemn representations to the United States concerning the above-mentioned bill.

答：中方曾多次就上述法案向美方提出严正交涉。

youdao

Foreign Minister Yang Jiechi also made "solemn representations" to North Korea's ambassador to China.

BBC: China media: Pyongyang pressure