"They broke their word to the world on ensuring the autonomy of Hong Kong", Mr Trump said from the White House, where he also blamed China for a "cover up" of the coronavirus outbreak.
Mr Trump's announcement on Hong Kong made on Friday in Washington, will mean that the city, now treated separately from mainland China in matters of trade and commerce, will be subject to United States tariffs on Chinese goods as part of the ongoing trade war.
In the run-up to Britain returning Hong Kong to China in 1997, a "one country, two systems" deal was forged to allow the city to maintain certain freedoms and autonomy for 50 years.
"This is the product of a plot by the external force and its vassal forces that seek the division and disintegration of China by tarnishing the image of a socialist country and fomenting and escalating a social disorder", the spokesperson added.
China's Foreign Ministry pledged on Wednesday to take all necessary countermeasures to address "foreign interference" regarding the national security law, a statement presumably aimed at the US.
Secretary of State Mike Pompeo on Wednesday informed Congress that the Trump administration would no longer consider Hong Kong to be separate under U.S. law, but it was up to Trump to spell out the consequences.
The president said Washington would also impose sanctions on individuals seen as responsible for "smothering - absolutely smothering - Hong Kong's freedom".
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A second Sacramento protest is underway at the state Capitol downtown Saturday morning, one of many in cities across the country. The protesters were forced back by police down Randolph St. and several people were seen being arrested on video.
The move has also rattled foreign investors, who fear the loss of the privileges that have allowed Hong Kong to thrive as a global financial hub. It means controls on exporting technology to Hong Kong.
He later signed a proclamation barring the entry of Chinese students tied to the Chinese military from entering the U.S.to study or conduct research above the undergraduate level, arguing Chinese "authorities use some Chinese students, mostly post graduate students and post-doctorate researchers, to operate as non-traditional collectors of intellectual property".
Mr Trump said last month the United States was suspending funding to the World Health Organization pending a review of the organisation.
Protests are simmering again as Hong Kong emerges from its coronavirus shutdown.
"I expect him to take some major steps that would show China he is serious, but not to change every U.S. law that applies to Hong Kong", he said. Demonstrators are expected to take to the streets on Sunday.
China has been the top source of foreign students to the United States for the past decade with almost 370,000 Chinese at USA universities, although Trump's order will not directly affect undergraduates.
Such attempts to interfere in Hong Kong affairs and China's internal affairs would not scare the Chinese people and were doomed not to succeed, it said, without explicitly naming the United States.