The emergency powers that Chief Executive Carrie Lam invoked last year to ban face masks at protests are a “missile launcher” which give the government “unrestricted nuclear power” to do whatever it wants, the Court of Final Appeal was told on Tuesday.

This was the argument put forward by Senior Counsel Gladys Li, who is acting on behalf of around 20 pan-democratic figures, including disqualified lawmaker Dennis Kwok, as they challenge the mask ban.

The chief executive invoked the Emergency Regulations Ordinance in October last year for her mask ban.

But the High Court later ruled that the ban was unconstitutional, before the Court of Appeal found it was only constitutional for the government to prohibit the wearing of masks at unauthorised assemblies, but not legal demonstrations.

Unhappy with the partial victory, the pro-democracy figures are now challenging the Court of Appeal ruling, as is the government.

Li told the top court that the colonial-era emergency legislation is unconstitutional as it gives too much power to the executive to launch subordinate regulations “under whatsoever circumstances”.

She noted that the mask ban came into effect within hours of it being gazetted, arguing that the move bypassed the legislative process and public participation in the making of law.

Li said it is up to the chief executive to determine what contributes an occasion of emergency or public danger, and this could give rise to abuse.

Another lawyer for some of the activists, Senior Counsel Johannes Chan, told the court that the scope of the mask ban is too wide, as it could cover those who are simply passing by a protest but not taking part in it.

Chan added that the ban was disproportionate as 70 percent of the protests last year were peaceful. He said it undermined people’s fundamental rights, especially those who wear masks for good reasons during peaceful assemblies.

“Protection of one’s health is a good reason to wear masks,” Chan said, pointing out that the community has been wearing masks for months in light of the Covid-19 pandemic.

Senior Counsel Benjamin Yu, who’s representing the government, said the CE is already required to have a factual basis to form her view as to what is an emergency or public danger.

He was expected to elaborate on the government's arguments on Wednesday.

The case is being heard by a five-judge panel, including Chief Justice Geoffrey Ma.

Speaking before the hearing, one of the appellants, pro-democracy activist and former lawmaker Leung Kwok-hung, urged judges on Hong Kong's top court to stand firm against pressure from the pro-Beijing camp and to maintain their independence.