Chinese President Xi Jinping chats with President Donald Trump during a welcome ceremony in Beijing on Nov. 9, 2017.

China threatened to retaliate after President Donald Trump signed two bills into law in support of Hong Kong protesters.

"China firmly opposes Hong Kong Act. We have made stern representations & strong protests to U.S.," Geng Shuang, a spokesman for the Chinese Foreign Ministry, said in a briefing Friday. "It is a stark hegemonic practice & a severe interference in Hong Kong affairs, which are China's internal affairs. China will take strong counter-measures."

Geng did not specify what those counter-measures would be, however.

Trump signed a bill into law on Wednesday that requires the State Department to certify annually that Hong Kong has sufficient autonomy to retain special U.S. trading consideration, which helps Hong Kong's economy. The second measure signed by Trump bars the sale of tear gas and rubber bullets to the Hong Kong police.