Hong Kong has once more descended into violence, with police firing teargas at protesters across the city as mass demonstrations calling for democracy entered their 10th consecutive week.

Clashes with police were particularly intense on Sunday night compared with previous days, as riot police fired teargas into a railway station to disperse crowds and were captured on film beating protesters with batons as they fled down an escalator in another station.

Quick guide What are the Hong Kong protests about? Show Hide Why are people protesting? The protests were triggered by a controversial bill that would have allowed extraditions to mainland China, where the Communist party controls the courts, but have since evolved into a broader pro-democracy movement. Public anger – fuelled by the aggressive tactics used by the police against demonstrators – has collided with years of frustration over worsening inequality and the cost of living in one of the world's most expensive, densely populated cities. The protest movement was given fresh impetus on 21 July when gangs of men attacked protesters and commuters at a mass transit station – while authorities seemingly did little to intervene. Underlying the movement is a push for full democracy in the city, whose leader is chosen by a committee dominated by a pro-Beijing establishment rather than by direct elections.

Protesters have vowed to keep their movement going until their core demands are met, such as the resignation of the city’s leader, Carrie Lam, an independent inquiry into police tactics, an amnesty for those arrested and a permanent withdrawal of the bill. Lam announced on 4 September that she was withdrawing the bill. Why were people so angry about the extradition bill? Beijing’s influence over Hong Kong has grown in recent years, as activists have been jailed and pro-democracy lawmakers disqualified from running or holding office. Independent booksellers have disappeared from the city, before reappearing in mainland China facing charges. Under the terms of the agreement by which the former British colony was returned to Chinese control in 1997, the semi-autonomous region was meant to maintain a “high degree of autonomy” through an independent judiciary, a free press and an open market economy, a framework known as “one country, two systems”. The extradition bill was seen as an attempt to undermine this and to give Beijing the ability to try pro-democracy activists under the judicial system of the mainland. How have the authorities responded? Beijing has issued increasingly shrill condemnations but has left it to the city's semi-autonomous government to deal with the situation. Meanwhile police have violently clashed directly with protesters, repeatedly firing teargas and rubber bullets. Beijing has ramped up its accusations that foreign countries are “fanning the fire” of unrest in the city. China’s top diplomat Yang Jiechi has ordered the US to “immediately stop interfering in Hong Kong affairs in any form”. Lily Kuo and Verna Yu in Hong Kong

Other protesters were injured as undercover riot police turned on a crowd in Causeway Bay and began to arrest people, while widely circulated photos on social media showed one woman bleeding profusely from her eye after she was hit by police fire at another demonstration. Police also suffered casualties, according to authorities.

It came as Cathay Pacific bowed to pressure from China, sacking two ground crew and suspending a pilot for “misconduct” in supporting the Hong Kong pro-democracy protests.

The Hong Kong flag carrier airline, whose biggest shareholder is the Swire Group, chaired by the British billionaire Barnaby Swire, said it had fired two ground staff members for allegedly leaking the travel arrangements for a Hong Kong police football team travelling to the mainland for a tournament.

The company said it was “aware of the inappropriate behaviour of an employee involving the misuse of company information” after a Cathay employee was accused by the Chinese state of posting details of the Hong Kong police officers travelling on the airline. The airline also said it had suspended a pilot who took part in pro-democracy protests, and faces charges for rioting. Cathay said the pilot was removed from flying duties on 30 July.

Cathay said it would also comply with a directive from Beijing banning all staff who support the protests from working on flights to the mainland or through its airspace. China’s aviation regulator has ordered the airline to hand over identifying information for staff on mainland-bound flights effective immediately.

The airline told all staff that it viewed the demonstrations as “illegal protests”, and if they took part they would be banned from flights. “Cathay Pacific Group’s operations in mainland China are key to our business. In addition to flying in and out of mainland China, a large number of our routes both to Europe and to the USA also fly through mainland China airspace,” its chief executive, Rupert Hogg, said.

Play Video 0:38 Hong Kong police fire teargas in city centre as clashes intensify - video

The luxury fashion label Versace and its artistic director, Donatella Versace, apologised to China after one of its T-shirts was criticised for identifying the semi-autonomous regions of Hong Kong and Macau as countries.

On a tumultuous day in the city, protesters dressed in protective masks and goggles with long-sleeved shirts and trousers to protect them from teargas moved back and forth across the city’s subway system as police pushed crowds from one neighbourhood to the next. Chants such as “Liberate Hong Kong, the revolution of our time” rang out as demonstrators filed into escalators alongside commuters and baffled tourists.

“They sacrifice themselves,” an admiring bystander said as groups of young protesters crowded into his subway carriage bound for the Kowloon peninsula to reinforce a police-protester standoff. “What they gain is for [all of] us.”

At Kwai Fong station, police fired teargas to disperse crowds. Earlier, they used batons to try to stop protesters.

Police said one officer had been injured by a petrol bomb hurled by a protester in Tsim Sha Tsui and that bricks had also been hurled at officers.

Protests, clashes and lack of trust: the new normal for Hong Kong Read more

While many in Hong Kong appear to support the protesters, including ordinary people who have shown up in their hundreds of thousands at peaceful marches this summer, its chief executive, Carrie Lam, has maintained that protesters are largely violent fringe elements who have taken advantage of a civil disobedience movement.

Beijing has also signalled that it is losing patience with the protests. Its Hong Kong affairs department has spoken to the media twice in recent weeks to warn protesters that their actions will not be tolerated.

Protests began in Hong Kong in early June when Lam attempted to push through a legislative bill that would have allowed for residents to appear before criminal courts in mainland China. Many residents saw the bill as a wedge issue that would lead to their loss of civil and political rights, promised until 2047 under the “one country, two systems” agreement.

The bill prompted the largest demonstrations since Hong Kong returned to Chinese rule in 1997, but Lam has steadfastly refused to meet any demands beyond a promise that the bill is now “suspended”.

Quick guide Democracy under fire in Hong Kong since 1997 Show Hide Hong Kong’s democratic struggles since 1997 1 July 1997: Hong Kong, previously a British colony, is returned to China under the framework of “one country, two systems”. The “Basic Law” constitution guarantees to protect, for the next 50 years, the democratic institutions that make Hong Kong distinct from Communist-ruled mainland China. 2003: Hong Kong’s leaders introduce legislation that would forbid acts of treason and subversion against the Chinese government. The bill resembles laws used to charge dissidents on the mainland. An estimated half a million people turn out to protest against the bill. As a result of the backlash, further action on the proposal is halted. 2007: The Basic Law stated that the ultimate aim was for Hong Kong’s voters to achieve a complete democracy, but China decides in 2007 that universal suffrage in elections for the chief executive cannot be implemented until 2017. Some lawmakers are chosen by business and trade groups, while others are elected by vote. In a bid to accelerate a decision on universal suffrage, five lawmakers resign. But this act is followed by the adoption of the Beijing-backed electoral changes, which expand the chief executive’s selection committee and add more seats for lawmakers elected by direct vote. The legislation divides Hong Kong's pro-democracy camp, as some support the reforms while others say they will only delay full democracy while reinforcing a structure that favors Beijing. 2014: The Chinese government introduces a bill allowing Hong Kong residents to vote for their leader in 2017, but with one major caveat: the candidates must be approved by Beijing. Pro-democracy lawmakers are incensed by the bill, which they call an example of “fake universal suffrage” and “fake democracy”. The move triggers a massive protest as crowds occupy some of Hong Kong’s most crowded districts for 70 days. In June 2015, Hong Kong legislators formally reject the bill, and electoral reform stalls. The current chief executive, Carrie Lam, widely seen as the Chinese Communist party’s favoured candidate, is hand-picked in 2017 by a 1,200-person committee dominated by pro-Beijing elites. 2019: Lam pushes amendments to extradition laws that would allow people to be sent to mainland China to face charges. The proposed legislation triggers a huge protest, with organisers putting the turnout at 1 million, and a standoff that forces the legislature to postpone debate on the bills. After weeks of protest, often meeting with violent reprisals from the Hong Kong police, Lam announced that she would withdraw the bill. Photograph: Dale de la Rey/AFP

Many of its detractors, including a number of retirees and families, returned to Victoria Park in the thousands on Sunday afternoon for an assembly against the bill and to repeat their oft-heard demands that Lam withdraw it permanently and step down.

At about 5pm, many pushed out of the park despite a police ban and into the shopping district of Causeway Bay and down Hennessy Road where they gathered close to police headquarters.

“We are aware of what will happen,” a protester, Cherry Tsang, said as she prepared to leave Victoria Park, “but I think it is actually freedom of speech.”

Ting Wai Fong, a retiree, said she was determined to keep coming to protests and march through the city to support the young generation.

She said protesters now faced the dual terror of arrest and imprisonment as well as mobs of pro-China supporters, who attacked journalists including a reporter with the public broadcaster RTHK on Sunday and clashed with protesters the previous week. “If we are afraid, if we are not coming out to rally, we are encouraging these people to spread the terror,” she said.

As thousands brought traffic to a standstill on Hong Kong island, a smaller simultaneous demonstration at Sham Shui Po in Kowloon was the first to be hit with police teargas.

Similar standoffs followed near police headquarters before the mostly young protesters decamped en masse for the Kowloon peninsula where many had already barricaded an important cross-harbour tunnel.

Protests looked likely to continue well into the night with police stationed at a number of subway exits across the city in apparent preparation to tackle new flashmob protest tactics.