Thousands of demonstrators marched in Hong Kong on Saturday, facing the threat of arrest and increasingly severe warnings from Beijing.

Protesters clad head to toe in black, carrying umbrellas and orange helmets, deviated from the route approved by police and took over a major road of the normally busy shopping district of Mongkok. One group held a black banner with the words: “The police have overstepped”, while others chanted for the release of protesters who have been arrested over the last two months of demonstrations.

Shops were closed in normally busy Mongkok as thousands took to the streets. Photograph: Philip Fong/AFP/Getty Images

“We are still fighting for our demands. Honestly, it’s tiring but it’s our duty and our responsibility,” said Jacqueline Chan, 17. “We are Hong Kong people. We live here. We were born here. Although it’s tiring we must come out and fight for our freedom.”

A protester waves a British flag in Mongkok on Saturday. Photograph: Jérôme Favre/EPA

Shops along the main road were closed and residents crowded the pavements watching demonstrators. Some handed out juice boxes and snacks while others cheered. Protesters distributed protective gear such as face masks, in the event of clashes with police, who have used teargas on demonstrators.

The previously banned march was sanctioned by the police at the last minute and is one of several protests this weekend in Hong Kong.

A marcher’s sign reads ‘Carrie Lam condemned by history’. Protesters remain angry over her support of the extradition bill. Photograph: Vincent Thian/AP

As the city enters its ninth consecutive week of protests, the movement shows few signs of abating, as public anger at the government spreads to more parts of Hong Kong society.

Thousands of civil servants, medical workers and staff from the city’s finance sector rallied on Thursday and Friday, while further protests were planned through the weekend. Demonstrators have also called for a citywide strike on Monday, which has already been backed by major businesses and unions.

The protests, which began over a proposal to allow extradition to China, pose the most serious challenge to China’s authority over the city since 1997, when it was returned from British to Chinese control.

In recent days, Beijing has ramped up its condemnation of the protests, which it describes as “riots”, and has accused the US and other western powers of instigating the unrest to hurt China.

On Thursday, Chen Daoxiang, the head of the Chinese army garrison in Hong Kong, said the military was “determined to protect [the] national sovereignty” of Hong Kong and would help put down the “intolerable” unrest if requested. The army released a promotional video showing tanks and soldiers firing on citizens in an anti-riot drill.

Hong Kong police on Thursday also charged 44 people linked to the protests with “rioting”, a crime that carries a maximum penalty of 10 years in prison. On online forums there were claims that police decided to allow the previously banned protest in Mongkok in order to surround demonstrators and arrest them en masse.

Others are increasingly worried about violence and escalating police tactics, which have included firing rubber bullets as well as teargas. Police were reportedly testing out water cannons.

“People are getting more scared,” said Chan. “But it will not change what we do. We will not [stop] because of fear.”

“Every time I think it may be the last time but I try my best,” said another protester who asked not to give her name.

Quick Guide What are the Hong Kong protests about? Show 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

Despite the arrests and warnings, demonstrators appear to be escalating and shifting their tactics. Over the last week, dozens have surrounded police stations where the arrested are believed to be held. Others appear to be focused on gathering more support among the public, or targeting international audiences.

Pro-Beijing supporters attend a rally to support the police and call for an end to violence in Hong Kong on Saturday. Photograph: Kim Kyung-Hoon/Reuters

“If peaceful marches that disrupt the road for an afternoon or so don’t work, maybe it spills over to blockading more roads, maybe for long. If that doesn’t work? Maybe next time people would besiege a government building ... It goes on and on,” said one protester, who asked to only give his first name, Chris.

“It’s like a hydra – whether it grows more heads, or its feet have become more threatening, the whole hydra has become a bigger threat.”

Despite the interruptions, large swathes of the public appear sympathetic to the protesters, with many pledging to join the strike on Monday. Some residents have organised a donation drive, for clothes of any colour other than black, for protesters to quickly change out of their signature all black outfits and avoid being picked out by police.

On Saturday, groups representing almost two dozen sectors, from retail to construction and engineering, issued a joint letter of their intention to strike on Monday. The statement condemned authorities for turning “a deaf ear to peaceful protests from a wide section society” and threatened more actions.

“If the government does not respond … we shall launch more and larger strikes and non-cooperation movements. We shall never give up until we succeed,” it said.