Secretary Lam said he believed that internet platform operators, such as Google, would comply with the court order to remove content related to the song, widely considered the unofficial anthem of the protests triggered by a now-shelved extradition bill.

Google said it was reviewing the judgment.

But hours after the Court of Appeal’s ruling in the afternoon, a Post check of several online platforms, including Google, YouTube and Apple’s iTunes, found search results for the song and options to play or download it.

The injunction bans “broadcasting, performing, printing, publishing, selling, offering for sale, distributing, disseminating, displaying or reproducing in any way” the tune with the intention to incite others to separate Hong Kong from the rest of the country, commit a seditious act or insult the national anthem, “March of the Volunteers”.

It also prohibits anyone from playing the song in a manner likely to cause it “to be mistaken as the national anthem insofar as the [Hong Kong Special Administrative Region] is concerned” or suggest the city “is an independent state and has a national anthem of her own”.

People could also be found guilty of contempt of court for helping or knowingly allowing others to participate in any of the stipulated acts.

In their written judgment, Chief Judge of the High Court Jeremy Poon Shiu-chor, Madam Justice Carlye Chu Fun-ling and Madam Justice Anthea Pang Po-kam said: “The composer of the song has intended it to be a ‘weapon’ and so it had become.

“It has the effect of justifying and even romanticising and glorifying the unlawful and violent acts inflicted on Hong Kong in the past few years, arousing and rekindling strong emotions and the desire to violent confrontations,” the judgment said.

“Further, in the hands of those with the intention to incite secession and sedition, the song can be deployed to arouse anti‑establishment sentiments and belief in the separation of the HKSAR from the [People’s Republic of China].”

The judges agreed there was a “compelling need” to grant the injunction to aid the criminal law for safeguarding national security, since the song was still freely available on the internet and remained prevalent.

Prosecutions alone were “clearly not adequate” to tackle acute criminal problems, they added.

“Such is the seriousness of the criminal problem that the court must intervene immediately to prevent the continuation of the prevailing unlawful state of affairs, otherwise any further damage to national security would likely be irreparable,” the judgment said.

The three judges also said the injunction was “necessary” to persuade internet platform operators to remove problematic videos in connection with the song from their platforms, as it was impracticable to bring proceedings against each unidentifiable person online.

To address the potential “engagement” of the right to free expression, exemptions were made for academic and journalistic purposes, the court noted.

“A civil injunction should be granted only if its assistance in terms of prevention of particular acts endangering national security is necessary to help the criminal law achieve its public interest purpose of safeguarding national security,” the court said.

It added the judgment was made after giving “great deference” to the executive’s assessment of national security, referring to a certificate issued by Chief Executive John Lee Ka-chiu that was binding on the courts under the Beijing-imposed national security law.

The city leader pronounced last July that criminal acts related to the song would pose national security risks, a month after Lam applied to the court for the injunction.

On Wednesday night, Lee said the injunction would safeguard national security and uphold the dignity of the national anthem.

“At the same time, it ensures that law-abiding citizens in Hong Kong can enjoy their freedoms and rights under the law,” he wrote.

Justice minister Lam defended the injunction order as having an “extremely narrow” scope, which would not restrict the free-flow of information nor any normal operation of any internet service providers in Hong Kong.

“Residents in Hong Kong have an expectation that relevant internet service providers will keep their word and follow through without any reasonable grounds to doubt their fulfilment of the commitments they have made,” he added, citing Google’s previous pledge to remove any illegal content.

Lam said his department would step up public education, as well as communication with internet platform operators, about the ban.

Senior Counsel Ronny Tong Ka-wah, a member of the key decision-making Executive Council, said that should any internet provider fail to comply with the injunction, legal action could be taken by the government if the operator had offices or representatives in Hong Kong.

“I suggest that everyone should refrain from downloading this song or placing it in any accessible platform for others to encounter,” Tong said.

In Beijing, foreign ministry spokesman Lin Jian told reporters that preventing anyone from using and disseminating the song with the intention of inciting national division and insulting the national anthem was a legitimate and necessary measure for the city to fulfil its constitutional responsibility of safeguarding national security and upholding the dignity of “March of the Volunteers”.

The Hong Kong government said on Wednesday night that relevant international covenants recognised that the law was able to impose reasonable and necessary restrictions on the exercise of rights such as freedom of speech and of the press to ­safeguard national security.

The appeal was the department’s second attempt to outlaw the circulation of the song, which has been mistakenly played instead of the national anthem at several overseas sports events.

Last year’s application at the Court of First Instance failed after Mr Justice Anthony Chan Kin-keung found the intended ban would run counter to established criminal justice procedures and would not compel Google, based in the United States, to censor the song as the government wanted.

The Court of Appeal on Wednesday said it agreed with Chan that the right to free expression was potentially engaged by the injunction because of the “chilling effects” on innocent parties.

But it did not agree with his findings and reasoning on the utility of the injunction, the compatibility with the criminal law and its contra-mundum effect, or it applying to anyone.

Created months into the social unrest, the song gained traction among young protesters with lyrics such as “liberate Hong Kong” and “revolution of our times”.