Hong Kong police fired tear gas and water cannons on Saturday as pro-democracy protesters threw gasoline bombs in the latest in a series of clashes 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 also threw bricks dug up from pathways at police.

The water cannon fired blue-dyed water, traditionally used elsewhere in the world to make it easier for police to identify protesters later.

Riot police then marched on foot toward the neighbouring Admiralty district, followed by about 20 police cars, where some protesters had thrown fire bombs from flyovers, some landing close to police. Others shone blue and green lasers at police lines.

Adrienne Arsenault reports from Hong Kong on how the arrests of prominent activists could increase tensions:

After 13 weeks of protests in Hong Kong, tensions between demonstrators and Beijing are as high as ever. The arrests of prominent, pro-democracy activists will likely be a flashpoint as people prepare for another tense weekend in the city. 5:58

There were rumours of one off-duty police officer being wounded.

In the neighbouring Wanchai bar and restaurant district, police fought running battles with protesters, some beating them with truncheons, according to Reuters witnesses. There were several arrests.

"We have to keep protesting. We cannot let China take back Hong Kong now," said Evelyn, a 25-year-old asset manager, who was among those chanting "gangster" at police outside a subway station across the harbour from the central business area in Kowloon district.

44-year-old Sze Sen-ming is blocking five police vans on Hennessy Road. The nurse says it’s not his first time blocking police vehicles.<br><br>“I did that for the next generation (of Hong Kong),” he says. “I have nothing to be scared of. It’s just a body.”<a href="https://twitter.com/hashtag/antiELAB?src=hash&ref_src=twsrc%5Etfw">#antiELAB</a> <a href="https://twitter.com/hashtag/ExtraditionLaw?src=hash&ref_src=twsrc%5Etfw">#ExtraditionLaw</a> <a href="https://t.co/PDLtjI1BrC">pic.twitter.com/PDLtjI1BrC</a> —@ezracheungtoto

Asked what she would do if authorities did not respond to protesters' demands, she said: "Maybe I will leave Hong Kong. I absolutely cannot live under Chinese rule."

The protests, which at one point blocked three key roads, came on the fifth anniversary of a decision by China to curtail democratic reforms and rule out universal suffrage in Hong Kong, a former British colony that was returned to China in 1997.

"The behaviours of the radical protesters gravely breach the public peace and pose a serious threat to the safety of police officers on duty and members of the public at the scene," the government said in a statement.

The People's Liberation Army 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.

Senior Chinese officials have warned that if the turmoil persists, "the central government must intervene."

Police were targeting MTR subway trains to make arrests, with TV footage showing people being beaten as they cowered on the floor behind umbrellas. Some rail lines were closed.

Injured passengers as riot police charged and pepper-sprayed the train carriages at Prince Edward MTR Station earlier on Saturday night.<br><br>In full: <a href="https://t.co/kmLJLFCnSX">https://t.co/kmLJLFCnSX</a>. Photo: Stand News via TVB live. <a href="https://twitter.com/hashtag/hongkong?src=hash&ref_src=twsrc%5Etfw">#hongkong</a> <a href="https://twitter.com/hashtag/hongkongprotests?src=hash&ref_src=twsrc%5Etfw">#hongkongprotests</a> <a href="https://twitter.com/hashtag/antiELAB?src=hash&ref_src=twsrc%5Etfw">#antiELAB</a> <a href="https://twitter.com/hashtag/china?src=hash&ref_src=twsrc%5Etfw">#china</a> <a href="https://t.co/mAfmropUsH">pic.twitter.com/mAfmropUsH</a> —@HongKongFP

Freedom religion and 'praying for justice'

Thousands took to the streets in the afternoon on a largely peaceful, meandering rally in the rain, many joining a "Christian march" from Wanchai 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. The crowds grew after dusk in Wanchai, where protesters built roadblocks and banged iron sticks. Firemen battled a huge fire outside a Methodist church in the main Hennessy Road where water canon were moving in.

People take part in the 'Prayer walk for Sinners' rally in Hong Kong on Saturday. Thousands of pro-democracy protesters defied a police ban on rallying, a day after several leading activists and legislators were arrested in a sweeping crackdown. In an attempt to sidestep the protest ban, crowds carried crosses and sang 'hallelujah' after calling on protesters to form religious gatherings, which do not require the same stringent permission from authorities. (Philip Fong/AFP/Getty Images)

The protests have gone on for three months, sometimes turning violent, and have targeted the airport, the legislature and the Liaison Office, the symbol of Chinese rule.

"Hong Kong has religious freedom," said Sally Yeung, 27, a Christian. "We are praying at different check points and praying for justice to arrive in Hong Kong.

"If they prosecute us simply because we are praying, they infringe our religious freedom."

Watch activist Joshua Wong as he vows the protests will continue:

Hong Kong activist Joshua Wong said he will not surrender even after he was arrested, charged with organizing an illegal protest and later released on bail. 0:44

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."

Water cannon vehicles used repeated to disperse protesters but they remain undeterred. <a href="https://twitter.com/hashtag/HongKongProtests?src=hash&ref_src=twsrc%5Etfw">#HongKongProtests</a> <a href="https://t.co/OxyHmgpTGR">pic.twitter.com/OxyHmgpTGR</a> —@frances_sit

Police erected water-filled plastic barriers around key government buildings and two water cannon, used briefly for the first time last weekend, were at the ready 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 said protesters vandalized the legislature.

'Be like water'

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."

Pro-democracy protesters march in the rain in central Hong Kong on Saturday. (Jae C. Hong/The Associated Press)

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.

President Xi and Carrie Lam just stay behind of water cannon and refuse to listen people’s voice. We all know it’s not the way out. <a href="https://t.co/m3VV1gx4sh">pic.twitter.com/m3VV1gx4sh</a> —@joshuawongcf

Beijing has also accused foreign powers, particularly the United States and Britain, of fomenting the demonstrations and warned against foreign interference.

Hong Kong returned to China under a "one country, two systems" formula that allows it to keep freedoms not enjoyed on the mainland, like the freedom to protest and an independent legal system.

There have been frequent clashes between protesters and police, who have often fired tear gas and rubber bullets to disperse crowds, amid accusations of excessive force.

Watch the evolution of the Hong Kong protests, on The National:

Over the course of 13 weeks the Hong Kong protests have evolved, their original goal has expanded and violence has escalated. Here's how we got here. 2:10

"A lot of people from the outside think it is the police who escalate [the violence] first," a police officer told a media briefing. "This is not true."

An off-duty policeman was attacked late on Friday night by three unidentified men with a knife in the Kwai Chung container port area, suffering wounds to his limbs and back, police said. The news was a top-trending topic on China's Twitter-like Weibo.

Protesters throw molotov cocktails outside the central government complex during clashes with police after an anti-government rally on Saturday in Hong Kong. (Chris McGrath/Getty Images)

With protesters and authorities locked in an impasse and Hong Kong facing its first recession in a decade, speculation has grown that the city government may impose emergency laws, giving it extra powers over detentions, censorship and curfews.

Lawmaker Fernando Cheung said the arrests of the three legislators were probably aimed at causing more anger and chaos to justify the use of emergency laws.

"To incite more people to come out today is totally ridiculous," he told Reuters.