American authorities on Wednesday formally notified Hong Kong that the United States has withdrawn from three bilateral deals with the semi-autonomous Chinese city on extradition and taxation.

The announcement follows President Donald Trump's decision to revoke Hong Kong's preferential trade status as Beijing clamped down on the territory over huge and often violent pro-democracy protests last year.

In July, Trump signed an executive order stipulating that Hong Kong lacked the autonomy needed to justify special treatment as compared with China.

"As part of the ongoing implementation measures, we notified the Hong Kong authorities on August 19 of our suspension or termination of three bilateral agreements," the State Department said in a statement. 

"These agreements covered the surrender of fugitive offenders, the transfer of sentenced persons, and reciprocal tax exemptions on income derived from the international operation of ships."

"These steps underscore our deep concern regarding Beijing's decision to impose the National Security Law, which has crushed the freedoms of the people of Hong Kong," it said.

Beijing imposed the new national security law in response to last year's pro-democracy protests.

It has described the law -- its contents kept secret until it was enacted on June 30 -- as a "sword" hanging over the heads of opponents in Hong Kong.

The law officially criminalizes secession, subversion, terrorism and colluding with foreign forces.

But the broadly worded provisions outlawed certain political speech overnight, such as advocating sanctions, and greater autonomy or independence for Hong Kong.