China summoned the U.S. ambassador on Thursday to "strongly protest" President Trump's signing of the Hong Kong Human Rights and Democracy Act in support of protesters, state media report.

Why it matters: Trump signed the bipartisan congressional bill condemning Chinese interference in Hong Kong's affairs and supporting the rights of pro-democracy protesters as Washington and Beijing hold crucial trade talks.

China's action came soon after the Chinese Foreign Ministry warned it would take "firm counter measures" if the U.S. continued to "interfere" in Hong Kong, per the New York Times.

What they're saying: A Chinese Foreign Ministry statement said the country's Vice Foreign Minister Le Yucheng told Ambassador Terry Branstad the U.S. bill marked a "serious interference in China’s internal affairs and a serious violation of international law," AP reports.

"We are officially telling the U.S. and the handful of opposition politicians in Hong Kong who follow America’s lead to not underestimate our determination to protect Hong Kong’s prosperity and stability, don’t underestimate our belief to protect the 'one country, two systems policy,'" the foreign ministry said in an earlier statement, translated by CNBC.

"And don’t underestimate our capabilities and strategies in protecting our country’s sovereignty, safety, growth and rights."

Go deeper: Pro-democracy parties triumph in key Hong Kong elections

Editor's note: This article has been updated with new details throughout.