China has unveiled new powers to censor Hong Kong's internet and access user data using its feared national security law -- but US tech giants have put up some resistance citing rights concerns.

The online censorship plans were contained in a 116-page government document released on Monday night that also revealed expanded powers for police, allowing warrantless raids and surveillance for some national security investigations.

Certain political views, slogans and signs became illegal in Hong Kong overnight with the passage of China's new national security law for the city Certain political views, slogans and signs became illegal in Hong Kong overnight with the passage of China's new national security law for the city Photo: AFP / ISAAC LAWRENCE

China imposed the law on semi-autonomous Hong Kong a week ago, targeting subversion, secession, terrorism and colluding with foreign forces -- its wording kept secret until the moment it was enacted.

Despite assurances that only a small number of people would be targeted by the law, the new details show it is the most radical change in Hong Kong's freedoms and rights since Britain handed the city back to China in 1997.

Late Monday, US Secretary of State Mike Pompeo spoke out against "Orwellian" moves to censor activists, schools and libraries since the law was enacted.

With certain phrases now outlawed in Hong Kong, protestors are finding creative ways to express their annoyance with Beijing With certain phrases now outlawed in Hong Kong, protestors are finding creative ways to express their annoyance with Beijing Photo: AFP / ISAAC LAWRENCE

"Until now, Hong Kong flourished because it allowed free thinking and free speech, under an independent rule of law. No more," Pompeo said.

Hong Kong Chief Executive Carrie Lam, who up until the imposition of the law in Hong Kong refused to talk about it, says her government will 'vigorously implement' it now Hong Kong Chief Executive Carrie Lam, who up until the imposition of the law in Hong Kong refused to talk about it, says her government will 'vigorously implement' it now Photo: AFP / ISAAC LAWRENCE

Under its handover deal with the British, Beijing promised to guarantee until at least 2047 certain liberties and autonomy not seen on the authoritarian mainland.

Years of rising concerns that China's ruling Communist Party was steadily eroding those freedoms birthed a popular pro-democracy movement, which led to massive and often violent protests for seven months last year.

China has made no secret of its desire to use the law to crush that democracy movement.

WhatsApp was among US tech giants that said it would deny requests for information from Hong Kong government and law enforcement agencies while it looks at the new law WhatsApp was among US tech giants that said it would deny requests for information from Hong Kong government and law enforcement agencies while it looks at the new law Photo: AFP / Lionel BONAVENTURE

"The Hong Kong government will vigorously implement this law," Chief Executive Carrie Lam, the city's Beijing-appointed leader, told reporters on Tuesday.

"And I forewarn those radicals not to attempt to violate this law, or cross the red line, because the consequences of breaching this law are very serious."

Hong Kong's police force has been granted vastly expanded powers to conduct warrantless raids and surveillance -- as well as issue internet takedown notices -- under Beijing's new national security law. Hong Kong's police force has been granted vastly expanded powers to conduct warrantless raids and surveillance -- as well as issue internet takedown notices -- under Beijing's new national security law. Photo: AFPTV / James HOSSACK

With pro-democracy books quickly pulled out of libraries and schools, the government signalled in the document released on Monday night that it would also expect obedience online.

Police were granted powers to control and remove online information if there were "reasonable grounds" to suspect the data breaches the national security law.

Internet firms and service providers can be ordered to remove the information and their equipment can be seized. Executives can also be hit with fines and up to one year in jail if they refuse to comply.

Riot police have become a common sight on the streets of Hong Kong Riot police have become a common sight on the streets of Hong Kong Photo: AFP / DALE DE LA REY

The companies are also expected to provide identification records and decryption assistance.

However the biggest American tech companies offered some resistance.

Facebook, Google and Twitter said Monday they had put a hold on requests by Hong Kong's government or police force for information on users.

Facebook and its popular messaging service WhatsApp would deny requests until it had conducted a review of the law that entailed "formal human rights due diligence and consultations with human rights experts," the company said in a statement.

"We believe freedom of expression is a fundamental human right and support the right of people to express themselves without fear for their safety or other repercussions," a Facebook spokesman said.

Twitter and Google told AFP that they too would not comply with information requests by Hong Kong authorities in the immediate future.

Twitter told AFP it had "grave concerns regarding both the developing process and the full intention of this law".

Tik Tok, which is owned by Chinese company Byte Dance, announced it was pulling out of Hong Kong altogether.

"In light of recent events, we've decided to stop operations of the TikTok app in Hong Kong," TikTok told AFP.

Tik Tok has become wildly popular amongst youngsters around the world. However many Hong Kongers have distrusted it because of its Chinese ownership.

ByteDance has consistently denied sharing any user data with authorities in China, and was adamant it did not intend to begin to agree to such requests.

In less than a week since the law was enacted, democracy activists and many ordinary people have scrubbed their online profiles of anything that China may deem incriminating.

Police officers will be able to conduct a search without a warrant if they deem a threat to national security is "urgent".

"The new rules are scary, as they grant powers to the police force that are normally guarded by the judiciary," barrister Anson Wong Yu-yat told the South China Morning Post.