Tearing a page out of ancient Chinese military philosophy, black-clad protesters in Hong Kong changed tactics and wreaked havoc by popping up in small groups in multiple locations across the city on Sunday, pursued by but also often eluding police who made scores of arrests.

Key points: Chinese president Xi Jinping issued a strong threat at a press conference in Nepal, warning of "crushed bodies" for dissenters

Chinese president Xi Jinping issued a strong threat at a press conference in Nepal, warning of "crushed bodies" for dissenters Violence escalated again in Hong Kong, with a police officer taken to hospital with a slashed neck and another man beaten

Violence escalated again in Hong Kong, with a police officer taken to hospital with a slashed neck and another man beaten Protesters employed new guerrilla-like tactics, eluding police in smaller groups at multiple locations

Violence spiralled as protests stretched from Sunday afternoon into the night, with police struggling to restore order.

On a state visit to Nepal on the same day, Chinese President Xi Jinping issued a strong threat against dissent, warning that independence advocates anywhere in China would be crushed.

The Chinese President issued a strong threat against dissent, warning that independence advocates attempting to "divide China" would be crushed. (AP via The Rising Nepal: Bikash Dware)

"Anyone attempting to split China in any part of the country will end in crushed bodies and shattered bones. And any external forces backing such attempts at dividing China will be deemed by the Chinese people as pipe-dreaming," he was quoted by state media.

Police said an officer was taken to hospital bleeding profusely after his neck was slashed, while local television networks also broadcast footage of a man in another district who was beaten bloody by protesters after they found a baton in his bag and suspected him of being an undercover officer.

Police have increasingly posed as protesters, scoring some tactical successes and sparking widespread paranoia among frontline demonstrators.

Throughout the cat and mouse battles on Sunday officers made dozens of arrests as they rushed to intercept activists, but the confrontations were generally less intense than earlier this month when the city was virtually shut down by the most serious unrest of the four-month protest movement.

Watch Duration: 31 seconds 31 s Hong Kong police are attacked by protesters during continuing riots in the city.

Video broadcast on Hong Kong television also showed a masked, black-clad protester dropping a riot officer with a flying high kick, followed by two other protesters who beat the officer on the ground and tried unsuccessfully to snatch his gun.

The guerrilla-like tactics sought to maximize the disruption and visibility of protests at a time when anti-government demonstrations have, as a whole, been showing signs of flagging as they stretch into a fifth month.

Pressure from a government ban on the face masks worn by many protesters and extreme violence earlier this month appear to have cooled the ardour of some demonstrators and whittled down protest numbers.

Online calls for gatherings to start at 2:00pm in dozens of malls, parks, sports grounds and other locations triggered an afternoon of mayhem and marked a shift from earlier more concentrated rallies in fewer spots.

Protesters changed tactics and popped up in small groups in multiple locations across the city, pursued by police who swooped in to make muscular arrests (AP: Kin Cheung)

"We're going to be more fluid and flexible," said Amanda Sin, 23, an office worker who joined a peaceful protest outside police headquarters in central Hong Kong.

"We are interchanging different tactics."

Roaming clumps of hardcore protesters — too numerous, elusive and fast-moving to be policed — popped up out of nowhere, vandalising stores, blocking traffic with makeshift barricades and spraying protest graffiti, often holding up umbrellas to shield their activities from view.

Throughout the cat and mouse battles on Sunday officers made dozens of arrests as they rushed to intercept activists (Reuters: Tyrone Siu)

Masked protesters wielding hammers wrecked a Huawei store that was apparently targeted because of the brand's links to mainland China.

On another store broken into and trashed, protesters sprayed, "We are not stealing."

The words "black heart" were sprayed in black inside a vandalised Starbucks, another frequent target of the anti-government and anti-China protests that have gripped the semi-autonomous Chinese territory since June.

Hong Kong protesters shifted tactics, using guerrilla-like tactics sought to maximize the disruption and visibility of protests (AP: Kin Cheung)

Changing strategies to adapt to shifting circumstances is a notion deeply engrained in Chinese thinking, notably detailed in Sun Tzu's ancient military treatise The Art of War, and inspiring Mao Zedong's Communist revolutionaries on their route to seizing power in China in 1949.

In Hong Kong, protesters speak of being "like water," fluid and adaptable.

"It's a guerilla-kind of demonstration," said Edmund Tang, 59, who slept overnight at the rally outside police headquarters that started Saturday and was still going strong Sunday with about 200 people, many of them retirees.

He said the week-old ban that makes the wearing of masks at rallies punishable by one year in jail dissuaded some demonstrators who had taken part in larger previous demonstrations.

"It's no longer possible to get 100,000 people to come out," he said, adding that the idea of protesting in small, diffuse groups was in part aimed at complicating policing efforts.

"Keep the hunt dogs running everywhere, getting crazier and crazier, without catching the prey. That's best," he said.

Protests that started in June over a now-shelved extradition bill have since snowballed into an anti-China campaign. (AP: Kin Cheung)

Police adapted, too, fanning out in multiple locations and quickly making arrests.

Speeding police vans were on the scene within minutes after black-clad protesters set up a makeshift roadblock in a shopping district in Kowloon.

One van rammed through a barricade of piled-up bamboo poles and officers sprinted off in pursuit of suspects.

Police pinned detainees to the floor and hauled them away. In one incident, officers fired tear gas rounds from a van before speeding away.

Other patrols pointed riot-control guns and cans of pepper spray to keep crowds at bay and hammered on their plastic riot shields as they cleared streets.

Bystanders responded with torrents of abuse.

One of the largest gatherings brought several hundred people together in a shopping mall in Shatin. A masked protester played the saxophone.

On the closed metal shutters of a subway station, another protester dressed head-to-toe in black sprayed, "When dictatorship is a fact, revolution becomes our duty."

Before dawn Sunday, protesters also clambered up a peak and erected a four-metre-tall white statue of a demonstrator in a gas mask, dubbed "The Lady Liberty of Hong Kong," that gazed over the restive city.

The protests gripping the international business hub began in response to a now-withdrawn extradition bill that would have allowed criminal suspects to be sent for trial in Communist Party-controlled courts in mainland China.

The movement then ballooned to encompass broader clamours for universal suffrage, an independent inquiry of the policing methods used against protesters and other demands.

Protesters also clambered up a peak and erected a four-metre-tall white statue of a demonstrator in a gas mask, dubbed "The Lady Liberty of Hong Kong". (AP: Kin Cheung)

AP