HONG KONG (REUTERS) - The Chinese Communist Party said it would "perfect" the system for choosing the leader of Hong Kong after months of anti-government protests as police in the ex-British colony fired water cannon to break up a Guy Fawkes-themed march.

The party said in a statement it would support its "special administrative region" of Hong Kong, which was handed back to China in 1997, and not tolerate any "separatist behaviour" either there or in neighbouring Macau, an ex-Portuguese colony that returned to Chinese rule in 1999.

Some protesters in Hong Kong have called for independence in sometimes violent unrest, a red line for Beijing. China denies meddling.

As the party statement was released by Xinhua news agency, Hong Kong leader Carrie Lam said she had a short meeting with Chinese President Xi Jinping in Shanghai.

"He expressed care and concern about Hong Kong, especially given the social disturbances that we have seen in the last five months and he expressed support for the various action taken by Hong Kong Special Administrative Region government," she told reporters.

Referring to the foundation of the 1997 deal under which Hong Kong reverted to Chinese rule, Mrs Lam said: "In strict accordance with the principle of 'one country, two systems' (we will continue) upholding the rule of law and trying to put an end to the violence."

The "one country, two systems" formula guarantees Hong Kong's freedoms, including an independent judicial system, for 50 years.

She denied widely reported rumours that the Hong Kong government was considering an amnesty for protesters charged with offences.

After gatecrashing fancy-dress Halloween festivities on Oct 31, a few hundred protesters marked Guy Fawkes Day on Tuesday (Nov 5) in the Tsim Sha Tsui tourist district of Kowloon by wearing the white, smiling Guy Fawkes masks made popular by anti-establishment hackers, the film V For Vendetta and protesters globally.

Some protesters vandalised traffic lights and a restaurant perceived as being pro-Beijing, prompting police to move in with the water cannon, near the science museum, as they have done on many nights during five months of demonstrations. Some protesters were detained while others ran off.

Guy Fawkes Day, also called Bonfire Night, is celebrated with fireworks and bonfires every Nov 5 in Britain, when effigies of "guys" are burnt, marking the night in 1605 when Fawkes was arrested for a "gunpowder plot" to blow up Parliament.

"We are here to tell the government that we are not afraid of them and that they should be afraid of us," masked protester Pete, 27, said in front of the huge, harbourfront neon Christmas decorations.

Mrs Lam banned face masks last month, invoking colonial-era emergency powers for the first time in more than 50 years, but protesters have largely ignored the ruling.

HK NATIONAL SECURITY

China's Communist Party, in a lengthy statement about decisions reached at a key leadership meeting known as a plenum last week, said it would improve the national security system in Hong Kong, as well as in Macau, though it gave no details.

The party decided to "establish a robust legal system and enforcement mechanism to safeguard national security in the special administrative regions and support them to strengthen law enforcement".

The party will "perfect" the appointment and dismissal mechanisms for the leaders and senior officials of the two territories, it added, reiterating comments from a Chinese Parliament official last week. Again, no details were given.

It will also "perfect" the system under which the party has full jurisdictional power over Hong Kong, in accordance with the Constitution, Xinhua said.

In a nod to some of the economic causes of the unrest, the party said it would support Hong Kong's economic development with a focus on resolving "deep-rooted" problems that affect social stability.

There will also be a focus on improving the "patriotic spirit" of young people and civil servants, the party said.

The demonstrations in Hong Kong began over a since-scrapped extradition Bill and escalated in mid-June against perceived Chinese meddling. Protesters have kept up their calls for universal suffrage and an independent inquiry into alleged police brutality, among other demands.

The protests, which pose the gravest challenge to Mr Xi since he came to power in 2012, have received broad support.

The number of people who take part in the mostly weekend rallies has dwindled from the millions who participated in June, but violence and vandalism have escalated. The authorities have refused permits for many recent protests, making them illegal from the outset and activists liable to be arrested.

There have been many injuries in the protests, but no deaths. A 22-year-old student at a Hong Kong university who fell during protests at the weekend was in critical condition on Tuesday, hospital authorities said.

Quoting sources, RTHK reported that the student is on life support. He was believed to have undergone two emergency operations and had part of his brain removed.

A man stabbed at least two people on Sunday and bit off part of a politician's ear before being beaten by protesters. A 48-year-old suspect has been charged with wounding.

Mrs Lam expressed her sympathies for the wounded, singling out the 22-year-old student.