UPDATE 7-China to "perfect" HK system as water cannon breaks up Guy Fawkes protest

* Asian financial hub rocked by months of street unrest

* Hong Kong leader says China president voiced concern for HK

* China says it will safeguard national security in Hong Kong (Recasts with water cannon)

By John Geddie and Kate Lamb

HONG KONG, Nov 5 (Reuters) - The Chinese Communist Party said on Tuesday 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 returned to China in 1997, and not tolerate any "separatist behaviour" either there or in neighbouring Macau, an ex-Portuguese colony that was handed back to Chinese rule two years later.

Some protesters in Hong Kong, angry at perceived Chinese meddling in its freedoms, have called for independence in sometimes violent unrest, a red line for Beijing. China denies interference.

As the party statement was released by Xinhua news agency, Hong Kong leader Carrie Lam said she had held 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, 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.

Lam denied widely reported rumours that her government was considering an amnesty for protesters charged with offences, one of the demands of the protesters. "In simple terms, it will not happen," she said.

BONFIRE NIGHT PROTESTS

After gatecrashing fancy-dress Halloween festivities on Oct. 31, hundreds of Hong Kong protesters marked Guy Fawkes Day on Tuesday 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.