HONG KONG - Hong Kong police fired tear gas and water cannon on Saturday as they tried to disperse pro-democracy protests that have plunged the Chinese-ruled city into its worst political crisis in decades.

Police fired round after round of tear gas as protesters took cover behind umbrellas between the local headquarters of China's People's Liberation Army and government HQ. Protesters threw bricks at police in return.

The clashes came on the fifth anniversary of a decision by China to curtail democratic reforms in the former British colony, which returned to China in 1997.

The PLA on Thursday rotated its troops in Hong Kong in what it said was a routine operation. Their Hong Kong HQ was the former base of the British military garrison.

People took to the streets on a largely peaceful, meandering rally, many joining a "Christian march" from the Wanchai entertainment district and congregating next to the Legislative Council, stormed by activists in an earlier protest.

Other demonstrators, many wearing black and face masks, marched in the Causeway Bay shopping district.

It was the latest in a string of protests over three months, some of which have turned violent, targeting the airport, the legislature and the Liaison Office, the symbol of Chinese rule.

Hovering under an umbrella outside the government offices, Eric, a 22-year-old student, said telling people not to protest was like telling them not to breathe.

"I feel it's my duty to fight for democracy," he said. "Maybe we win, maybe we lose. But we fight."

Police erected water-filled plastic barriers around key government buildings and two water cannon, used briefly for the first time last weekend, were parked near the Liaison Office, which was daubed with graffiti in an earlier protest.

The MTR subway suspended some services and shut station exits because of likely "public activities".

Police arrested a number of prominent pro-democracy activists and three lawmakers on Friday, seeking to rein in a movement which started with anger over planned legislation allowing extraditions to mainland China. It soon broadened into calls for democracy amid fears China is squeezing Hong Kong's freedoms.

But the latest protests have no leaders. The slogan is "be like water", meaning be flexible. Marchers on Saturday were marching here and there, wherever streets took them, communicating with different hand signals and chanting "stand with Hong Kong" and "fight for freedom".

Some said roadblocks were forcing marchers to splinter.

China denies the charge of meddling in Hong Kong, which it says is an internal affair. It has denounced the protests and warned of the damage to the economy.

China is eager to quell the unrest before the 70th anniversary of the founding of the People's Republic of China on Oct. 1 but protesters vandalized a long red banner celebrating the event to cheers from the crowd. -Reuters