Hong Kong police are set to start spraying liquid dye at crowds during potential future demonstrations to help them catch protesters who wear masks to conceal their identity.

Once sprayed onto a person at a demonstration site, the liquid dye could stay on their skin or clothing, which would make it easier for the police to identify relevant individuals if necessary, the police said.

Such liquid dye, said to be harmless and edible, could be added into water or tear gas solution, said a spokesperson.

One Hong Kong police officer demonstrates the new equipment in a video released on Sunday

Such liquid dye, said to be harmless and edible, can be added into water or tear gas solution

The liquid dye can be poured into a portable spraying device or a water jet pack to be used

The liquid dye can be poured into a portable spraying device or a water jet pack to be used by anti-riot officers, Superintendent Louis Lau Siu-pong explained in a video released by Hong Kong police on Sunday.

He stressed that the Hong Kong police have strict guidelines on using such spray and will choose different equipment to squirt it depending on the circumstances.

China warned Hong Kong's pro-democracy protesters today that 'those who play with fire will perish by it', a day after the most widespread unrest of the two-month crisis.

China warned Hong Kong's pro-democracy protesters today that 'those who play with fire will perish by it', a day after the most widespread unrest of the two-month crisis. Pictured, protesters stand behind barricades after occupied an express way during a rally on August 5

A total of 148 people aged between 13 and 63 have been arrested in connection with yesterday's protests. Pictured, protesters gather at an anti-extradition rally in Mong Kok

Hong Kong buckled under a general strike followed by the most widespread and sustained clashes so far at more than a dozen locations. Pictured, anti-extradition protesters throw bricks as others react after police fired tear gas at them during clashes in Wong Tai Shin

Police stations were a particular target, with protesters hurling stones, eggs and bottles, and using giant improvised slingshots to catapult bricks over walls. Pictured, protesters stand off against riot police at Wong Tai Sin when workers across the city staged a strike on August 5

Superintendent John Tse told reporters that police yesterday fired some 800 tear gas rounds - almost as many as the 1,000 rounds they said they had fired throughout the last two months. Pictured, teargas bullets are seen after clash at Wong Tai Sin on August 5

The city has been plunged into chaos by weeks of protests triggered by opposition to a planned law that would have allowed extraditions to mainland China. Pictured, demonstrators attend a rally to support the city-wide strike and to call for democratic reforms on August 5

In its harshest warning yet Beijing said the immense strength of the central government should not be underestimated as police in the semi-autonomous city announced they had arrested 148 people aged between 13 and 63 in connection with Monday's protests.

The city has been plunged into chaos by weeks of protests triggered by opposition to a planned law that would have allowed extraditions to mainland China. The protests have since evolved into a wider movement for democratic reform and the protection of freedoms.

A total of 486 protesters aged between 13 and 76 have been arrested since the mass demonstrations broke out on June 9. The suspects were accused of rioting, unlawful assemblies, assault on police officers, cyber-related crimes among others.

Police also said that at least 139 officers had been injured, including two who were still being hospitalised.

At a press briefing in Beijing, Yang Guang, spokesman for the Hong Kong and Macao Affairs Office of the State Council, said the 'radical protests... have severely impacted Hong Kong's prosperity and stability, pushing it into a dangerous abyss'.

Yang said the government still 'firmly supports' both the Hong Kong police force - who have been criticised for their handling of the protests - and Carrie Lam, the city's pro-Beijing leader who protesters want to resign.

Yang Guang (pictured), Beijing's spokesman for the Hong Kong and Macao Affairs Office of the State Council, said at a press conference today that the 'radical protests... have severely impacted Hong Kong's prosperity and stability, pushing it into a dangerous abyss'

Yang said the government still 'firmly supports' both the Hong Kong police force - who have been criticised for their handling of the protests - and Carrie Lam (pictured), the city's pro-Beijing leader who protesters want to resign. Lam has apologised twice over the bill

'We would like to make it clear to the very small group of unscrupulous and violent criminals and the dirty forces behind them: Those who play with fire will perish by it,' Yang said.

'Don't ever misjudge the situation and mistake our restraint for weakness... Don't ever underestimate the firm resolve and immense strength of the central government.'

Hong Kong police said 148 people were arrested during running battles with protesters on Monday as the city buckled under a general strike followed by the most widespread and sustained clashes so far at more than a dozen locations.

Police stations were a particular target, with protesters hurling stones, eggs and bottles, and using giant improvised slingshots to catapult bricks over walls. An apartment complex that houses police officers and their families also came under attack.

Superintendent John Tse told reporters that police fired some 800 tear gas rounds - almost as many as the 1,000 rounds they said they had fired throughout the last two months.

Meanwhile, three masked youngsters from the largely leaderless movement took the unusual step today of holding a press conference to demand democracy, liberty and equality, and condemn the city's pro-Beijing leaders.

Protesters from right, Jerry Chan, Linus Kim and Mary Tsang attend a press conference in Hong Kong on August 6. They condemned what they call the government's 'empty rhetoric' and instances of alleged police abuse in an inaugural 'People's Press Conference'

A protester throw a stone towards police outside in Tin Shui Wai during a protest on Monday

Protesters Jerry Chan, right, chats with Linus Kim during a press conference on August 6

Dressed in the movement's signature yellow construction helmets and hiding their identities with face masks, the two young men and one woman billed their gathering as a civilian press conference 'by the people, for the people'.

'We call on the government to return the power back to the people and to address the demands of Hong Kong citizens,' they said as they read out their statements in both English and Cantonese.

In Beijing, the press conference held by China's cabinet-level State Council was the second about the unrest in as many weeks, highlighting concern in the capital.

The clashes have piled pressure on Chinese President Xi Jinping, and led to speculation that Beijing might be forced to intervene in some capacity, even militarily.

Riot police fire tear gas at protesters during a demonstration in Wong Tai Sin on August 5

Protesters from right, Mary Tsang, Linus Kim and Jerry Chan listen to a question from a reporter during a press conference in Hong Kong

Police fire tear gas a demonstration in support of the city-wide strike and to call for democratic reforms at Tai Po residential area in Hong Kong on August 5

Yang, however, seemed to downplay any idea of mainland police or military helping with law enforcement, saying the Hong Kong government was 'fully capable of punishing the violent crime in accordance with the law, restore order to society, and restore stability to society'.

The protests on Monday paralysed the subway system during morning peak hour, led many shops to close and delayed scores of international flights.

In a press conference in Hong Kong, Lam warned the city was nearing a 'very dangerous situation' as she framed the protests as a challenge to China's sovereignty.

'I dare say they are trying to destroy Hong Kong,' said Lam.

The protesters have shown no sign of easing their campaign, however.