HONG KONG (NYTIMES) - When Hong Kong's leader invoked emergency powers to ban face masks during protests, she went to great lengths to explain that the city wasn't in a state of emergency. Rather, she declared, after months of unrest, the city was in a "very critical state of public danger".

The message, and the ban itself, was highly calculated. It was designed to show that the government was taking action to protect public safety while trying not to provoke more violence from protesters.

The pro-Beijing camp of government leaders and lawmakers, from moderates like Chief Executive Carrie Lam to the hardliners, was also determined to deal with the unrest, and not give the Chinese leadership any reason to intervene.

"We want to resolve it ourselves," said Ms Regina Ip, a hardline member of Mrs Lam's Cabinet who leads a political party that is popular with police officers.

Trying to restore public order without spurring more protests will be hard to achieve, however, and the city's leadership is already considering imposing other measures to crack down. Starkly different views on just the face-mask ban underscore how irreconcilable the differences between the government and the protesters have become.

To Hong Kong's top leaders, the ban, punishable by up to a year in prison, was a measured approach. It avoided for now the more extreme options proposed by some pro-Beijing hardliners, like far harsher sentences, running courthouses 24 hours a day or imposing a curfew.

To the protesters, the prohibition - targeting standard gear at demonstrations - is a manifestation of their worst fears, an erosion of the civil liberties that have differentiated the semi-autonomous territory from the rest of China. In their thinking, simply asserting the emergency powers is a worrisome sign that Beijing will exert ever more influence over the city.

After an eerie quiet pervaded the city last Saturday (Oct 5), tens of thousands of protesters returned on Sunday to march in the rain, defying the ban by wearing masks. While the marches started peacefully, protesters on the edges set up barricades, lit fires and vandalised shops whose owners they perceived to be supporters of Beijing.

Police fired many rounds of tear gas in an effort to disperse the crowds, and urged residents to stay home.

"The most disastrous thing is that you invoke an archaic, draconian, colonial piece of legislation made at a time, 1922, when Hong Kong did not have a mini-Constitution," said Mr Alan Leong, chairman of the pro-democracy Civic Party. "It is no longer rule of law; it is now rule by one woman."

For nearly two months, Mrs Lam and her top advisers vigorously debated how to tamp down the increasing violence. They consulted extensively with civil liberties and human rights lawyers within the government, as well as constitutional experts and security specialists.

The discussions continued last week in the hallways and restaurants of the opulent Grand Hyatt hotel in Beijing, where Mrs Lam's 240-member delegation stayed before attending China's National Day parade last Tuesday. Mrs Lam, at a news conference announcing the ban last Friday, made a point of emphasising that she did not discuss the issue with any Beijing officials during that visit.

To avoid potential protesters at Hong Kong's airport, Mrs Lam caught a flight on Tuesday afternoon to Shenzhen on the mainland border, then crossed over into the city. Just as she was arriving home, a police officer shot a protester in the chest at point-blank range.

The bullet barely missed the protester's heart, spine and major arteries.

"On the first of October, we were 3cm away from disaster," said Mr Ronny Tong, another member of Mrs Lam's Cabinet, the Executive Council.

With the shooting, Mrs Lam and her team believed that they had no choice but to invoke the colonial-era Emergency Regulations Ordinance. The law, which hadn't been used since deadly riots in the late 1960s, gives the chief executive extraordinary power to enact rules without going through the Legislature.

Other options, beyond the mask ban, are still under consideration if the chaos intensifies, according to advisers to Mrs Lam, several of whom spoke on the condition of anonymity, given the sensitivity of the issue. But the policy options all have their own limitations and the potential to further incite protesters.

A curfew is on the list, possibly targeted just at teenagers, whom the authorities have blamed for much of the recent violence. The British used a curfew in Hong Kong to restore order during rioting by pro-communist activists in 1967.

But imposing one now isn't entire practical. Protesters have shown a talent for moving quickly around the city, so the authorities would need a curfew for all neighbourhoods. And police, already stretched, don't necessarily have the resources to enforce it.

A second option, according to Mrs Lam's advisers, is to give police more time to hold suspects before they must be charged by prosecutors with a criminal offense or released. Currently, they have only 48 hours, which Hong Kong police say isn't enough time to investigate.

The British in 1967 took a far more drastic measure by suspending such limits. Back then, the authorities detained dozens of Maoist activists for half a year without charges at a special prison.

Human rights lawyers inside and outside the government have warned that any move towards longer detentions now may be struck down by Hong Kong's courts. More legal protections are available to residents under the Basic Law, a mini-Constitution issued in 1997, when Hong Kong was returned to the Chinese.

But the most likely policy option now being considered, several of Mrs Lam's advisers said, is to greatly extend the operating hours at Hong Kong courthouses so they can put numerous violent protesters behind bars quickly.

To that end, the Hong Kong leadership is closely studying the British government's response to lethal riots in 2011 in London's Tottenham neighbourhood and elsewhere around the country, said Prof Albert H.Y. Chen, a prominent law professor at Hong Kong University who advises Beijing on legal issues in the territory. During the unrest, Britain temporarily operated courts for 24 hours a day to quickly process a large number of people detained on accusations of arson, assaulting police officers and other offences.

It could be relatively easy to operate Hong Kong courts around the clock, since the city still has almost identical judicial rules to Britain, a legacy of more than 150 years of colonial rule. The main obstacle is Hong Kong's shortage of judges.

Attracting the city's top legal minds to become judges has been hard because they can earn more in the private sector, while the process for appointing new judges is long and contentious. Mrs Lam could bypass the process with her emergency powers and name a lot of young, pro-Beijing judges, but that would undermine Hong Kong's international reputation for judicial independence.

So far, the government is unwilling to go to the extreme of calling for intervention by Beijing.

An obscure provision under the Basic Law, Article 18, allows the mainland to extend its stringent national security laws to Hong Kong if the Standing Committee of China's rubber-stamp legislature "decides that the region is in a state of emergency".

Mrs Lam seemed to fend off this possibility when she emphasised last Friday that Hong Kong wasn't in such a dire position.

Still, Mr Lau Siu Kai, a former top city official who is a leading adviser to Beijing on Hong Kong policy, said that unrest had reached the point where Article 18 might become an option at some point.

Prof Lau cautioned, however, that he wasn't calling for it. Beijing, he said, did not want to intervene and become responsible for fixing Hong Kong's problems.

"That is the last thing Beijing wants to do," Prof Lau said. "Right now, Beijing is ready for a long, drawn-out war, because what is happening in Hong Kong is hurting Hong Kong more than the mainland."