Authorities in Hong Kong moved quickly to implement the new national security law, which went into effect at 11 pm Tuesday evening. As protesters defied a government ban on marches to commemorate the 23rd anniversary of the return of the city to Chinese rule, police arrested close to 400 people, including 10 under the new law. Police also held aloft flags stating that any protest activity would be considered a violation of the law. The first arrest under the national security law was of a man holding a “Hong Kong Independence” sign. However, upon closer look, observers noticed that he had cheekily included, in very small print, “No to” before the slogan.
People are pointing out that the flag appears to say, in tiny print, “no to” before “Hong Kong independence” and “不要” before “香港獨立.” Could make for a crazy test case https://t.co/HWjP4luZfV
— Austin Ramzy (@austinramzy) July 1, 2020
— Galileo Cheng (@galileocheng) July 1, 2020
this kid was waving a hk independeve flag, which is illegal and punishable by a lengthy jail term under the new #NationalSecurityLaw a couple of aunties slapped a cap on him to hide his face and lectured him on how dangerous what's he is doing was, but didn't stop him pic.twitter.com/PxrIc6TWG0
— teelerebane (@teelerebane2) July 1, 2020
Dan Strumpf, Mike Bird, and Joyu Wang at The Wall Street Journal report on the protests and the government response:
Hundreds of Hong Kong police officers moved in swiftly to quash dissent and implement the law, which gives Beijing much greater powers to police the city and punish those accused of subversion and supporting separatism. Police fired tear gas, pepper spray and water cannons to disperse protesters and raised a banner to warn them that they could be violating the new law.
At the end of the day—the anniversary of Hong Kong’s 1997 handover from British colonial rule—the protests had dissipated, and police had arrested about 370 people, including 10 under the new law, which one senior Chinese official described Wednesday as a birthday present to the city.
The protests highlight the difficulty Beijing faces in suppressing dissent in a city that has become a global financial hub built on rule of law and Western-style freedoms. The new security law, which carries penalties of up to life imprisonment, risks further inflaming anti-Chinese sentiments in the city and triggering responses from Western governments that have criticized it as the greatest erosion of the city’s promised autonomy since the handover. [Source]
If there is one city that refuses to sit by, idle and scared, while its freedoms are being dismantled, it is this one. https://t.co/rSFtvX65vN
— Shibani Mahtani (@ShibaniMahtani) July 1, 2020
Police water canon maliciously targets reporter on Hennessy Road. pic.twitter.com/kxeEOqtaUj
— Ryan Ho Kilpatrick 何松濤 (@rhokilpatrick) July 1, 2020
We are on street to against national security law. We shall never surrender. Now is not the time to give up. pic.twitter.com/E1mDMvtycc
— Joshua Wong 黃之鋒 ? (@joshuawongcf) July 1, 2020
— Jane Richards (@JaneRichardsHK) July 1, 2020
CNN has learned Hong Kong police have been instructed to arrest anyone chanting a slogan supporting Hong Kong or Taiwan independence, anyone in possession of a flag or banner promoting Hong Kong or Taiwan independence will also be arrested & prosecuted under the new nat sec law. pic.twitter.com/ImxvJMPyPE
— Will Ripley (@willripleyCNN) July 1, 2020
The "We really fucking love Hong Kong" banner from today's protest has already been turned into art. Major funeral vibes. pic.twitter.com/rlPWoC1baD
— Katharin Tai 戴愷琳 (@Whitey_chan) July 1, 2020
— Denise Ho (HOCC) (@hoccgoomusic) July 1, 2020
After the announcement of the new law, activists, writers, publishers, internet users, and others whose views don’t align with Beijing’s scrambled to remove any public expression of political opinion. Vivian Wang and Alexandra Stevenson report for The New York Times:
The law was proving effective in tamping down the anti-government demonstrations that have wracked Hong Kong for more than a year. On Wednesday, the anniversary of Hong Kong’s return to Chinese control — usually observed by huge pro-democracy marches — a scattered crowd of thousands protested, only to be corralled by the police and risk arrest for crimes that did not exist a day earlier.
[…] A museum that commemorates the 1989 Tiananmen Square massacre is rushing to digitize its archives, afraid its artifacts could be seized. Booksellers are nervously eyeing customers, worried they could be government spies. Writers have asked a news site to delete more than 100 articles, anxious that old posts could be used against them.
“You can say this law is just targeting protesters and anti-Chinese politicians, but it could be anyone,” said Isabella Ng, a professor at the Education University of Hong Kong who founded a charity that helps refugees in the city.
[…] “If you haven’t tasted what tyranny is, be prepared, because tyranny is not comfortable,” said Bao Pu, the founder of New Century Press, one of the city’s few surviving independent publishers. [Source]
Receiving a number of these messages this morning. Encrypted, private chats that don't, by and large, touch on sensitive issues. Sign that working as a journalist in Hong Kong will become much more like being in China. https://t.co/gQ0Rwl8eXK
— ????? ????????? ????????? (@jgriffiths) July 1, 2020
Several legal experts expressed concerns over the application of PRC law to Hong Kong under the guise of safeguarding national security, an apparent intrusion into Hong Kong’s autonomous legal system under the Basic Law. NPC Observer summarizes the main problems it sees with the new law:
Three aspects of the Law are particularly problematic: (1) its criminal provisions are worded in such a broad manner as to encompass a swath of what has so far been considered protected speech; (2) it provides for the direct application of mainland Chinese law—the notoriously restrictive Criminal Procedure Law [刑事诉讼法] no less—in Hong Kong in certain circumstances, outside the Annex III mechanism; and (3) it displaces certain core protections for the accused under Hong Kong law and grants the police sweeping investigative powers without judicial oversight. [Source]
In his analysis of the new law, legal scholar Donald Clarke notes that, “It’s not the substantive crimes and their definitions that count; it’s the institutions that will investigate, prosecute, and judge them that count.” To that point, he writes:
Article 48 is very important. It provides for the establishment within the territory of Hong Kong of a special Office for Safeguarding National Security. This Office is a mainland body like (for example) the Liaison Office, staffed by mainland officials appointed by mainland authorities. It has a number of functions, including, critically, the power to “handle” national security cases (Art. 49(4)). It can take jurisdiction over any case with the approval of the CPG (Art. 55). It can then send people back to China for processing (I suspect it would unduly dignify the proceedings to call them a “trial”) and sentencing in mainland institutions according to the Chinese Criminal Procedure Law (Art. 57). Article 56 says that the Supreme People’s Procuratorate will select the procuratorate that will prosecute, and the Supreme People’s Court will select the court that is to hear the case. (Just to be clear, in each case, the Law is clearly talking about mainland procuratorates and mainland courts.)
Let’s take a closer look at the powers of the Office and its personnel. Here we see something really remarkable. First, Article 57 states that with respect to measures undertaken according to law (this is not a meaningful qualifier) by the Office, relevant organs, organizations, and individuals must obey. Whatever the Office says, you must do. [Source]
In a previous blog post, Clarke wrote that under the law, staff of the Office for Safeguarding National Security are not bound by any law within Hong Kong or within mainland China, calling it “real Gestapo-level stuff.”
Wow. Didn't take long for China to announce that Art. 55 of the Nat Sec Law is completely meaningless. Trial on the mainland means the National Security Office has taken jurisdiction of the case. When does it do that? https://t.co/geWJQ1fEGN
— Donald Clarke 郭丹青 (@donaldcclarke) July 1, 2020
Jeremy Daum at China Law Translate points out that the law establishes a bifurcated criminal procedure under which mainland authorities can take control of national security cases and apply mainland law:
The Central government can authorize its National Security Office to take direct jurisdiction at the request of either Hong Kong’s Commission or the Office itself in any of three broad situations: 1) when the involvement of foreign forces makes it hard for Hong Kong to handle the case; 2) The Hong Kong government can’t effectively implement the law, and 3) when faced with significant real threats to national security. 
In these cases, the Office will conduct the investigation itself, and prosecutors and judges will be selected by the mainland’s Supreme Court and Procuratorate.  From investigation through the enforcement of penalties, the mainland Criminal Procedure Law will govern, including limiting access to an attorney to after the first interrogation or the imposition of ‘compulsory measures’. [57,58].
The work of the Office is told to comply with Hong Kong’s laws as well as national laws, under supervision of the mainland procuratorate, but is not subject to Hong Kong law or interference by local authorities. 
Both the local and central government jurisdictional paths apply only to certain types of crimes, namely: Separatism (secession), Subversion of State Power, Terrorism, and Collusion with Foreign or Taiwan Forces. The law breaks down the elements for each of these offenses, some of which include only speech or advocacy, and others rely on subjective assessments that may be difficult to apply. Terrorism, for example, includes conduct that is violent or destructive, but only when it is meant to further a political agenda through coercion or intimidation, a more subjective standard. [Source]
Some activists in Hong Kong now fear that their treatment will be no different from their counterparts in China. The New York Times’ Li Yuan interviewed social scientist, professor, and co-founder of Hong Kong’s 79-day Occupy movement Chan Kin-man about Hong Kong’s new reality:
I caught up with Mr. Chan after the passage of the national security law. “With the law, we’re living in a big prison,” he said. “There’s no difference between Hong Kong and Beijing now.”
In another sign of the rising anxiety level in Hong Kong, his new book, “Chan Kin-man: Letters from Prison,” sold 2,000 copies in presale and bookstore orders this month. Books like this usually sell only a few hundreds copies, he said.
The demand wasn’t only driven by an interest in the prison experience, he said. “Everyone needs to face the question: In an environment with diminishing freedom and growing suppression, how are we going to keep cool and not crash?”
As someone who dedicated his life to studying and building civil society, Mr. Chan said he was confident that in the long run Hong Kong would prove its resilience. People just needed time to adjust to the darkness, he added. [Source]
Chinese Foreign Ministry spokesperson Hua Chunying took to Twitter to defend the implementation of the law and to lash out at critics, notably the U.S.:
They are just worried about losing the right and freedom to use HK as a base and tool to hurt China's national security!
— Hua Chunying 华春莹 (@SpokespersonCHN) July 1, 2020
Canada, meanwhile, issued a travel warning for Hong Kong, stating that Canadian citizens “may be at increased risk of arbitrary detention on national security grounds and possible extradition to mainland China.”
See also “The ‘Restructuring’ of Hong Kong and the Rise of Neostatism” by Sebastian Veg for Toqueville21 for more about the erosion of Hong Kong’s legal guarantees “under the imperative of reasserting Chinese sovereignty.”