Protesters in Hong Kong have pledged to stand up to thugs who attacked demonstrators at the weekend as public anger grows towards the government and police.

Demonstrators have filed for a permit to hold a rally on Saturday in Yuen Long, the district on the outskirts of Hong Kong where dozens of masked men chased and beat commuters and protesters with wooden poles and metal rods, leaving at least 45 people in hospital. Police arrived after the assailants left.

Footage of the attack, which included a pregnant woman being hit, protesters being punched and kneed, and commuters screaming and crying while trying to shield themselves, emerged on Sunday night, fuelling further political unrest as demonstrators, opposition lawmakers and others demanded answers from authorities for failing to stop the violence.

Max Chung, who delivered the application for a letter of no objection from the police, that is required to hold a rally, said: “We want to show to the public and international community that Hong Kongers, we will never surrender in front of terrorism … To show our solidarity and say no to terrorism, we have to stand up.” Chung said: “Yuen Long was under terrorist attack and we have no choice but to take it back.”

The protests, principally over a controversial bill that would allow suspects to be extradited from Hong Kong to mainland China, have taken on new demands, including an investigation into police use of rubber bullets, teargas and physical violence against protesters.

Protesters are angry at the police’s slow response to the attack in Yuen Long and their pursuit of the case. Six people have been arrested for “unlawful assembly”.

The violence in Yuen Long has heightened tensions and fears of further attacks. On Tuesday evening, unverified footage showed men in white gathering in Tuen Mun, another city near Yuen Long in the New Territories. One video circulating online showed two men in white dragging a man in a black shirt across the road, but there were no reports of major disturbances.

Protesters and residents are also angry at the government’s weak condemnation of the violence. Hong Kong’s leader, Carrie Lam, said the “shocking violence” in Yuen Long would be investigated, but devoted most of her comments to criticising protesters, who surrounded Beijing’s liaison office in Hong Kong and defaced the national emblem of the People’s Republic of China on Sunday.

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“My team and I are here to show that while some of our work was not done properly … my colleagues and I have been making efforts to identify the root causes of this discontent,” she said.

Lam’s remarks failed to placate residents. On Tuesday, a group of aviation staff called for a protest at Hong Kong airport on Friday to condemn the government and police for “ignoring the random attacks on citizens in Yuen Long”. Other activists called for a strike from classes and work the following Monday if Lam does not respond to their demands. A group of medical workers has also called for a sit-in on Friday.

In Yuen Long, Chung and other protesters are demanding the government conducts an independent investigation and officially characterises the violence as a “cross-border terrorist attack”. Demonstrators believe some of the assailants were from mainland China.

As demonstrators circulated calls for the rally on Saturday, rumours of impending violence from residents or men wearing white spread, giving protesters pause.

Facebook Twitter Pinterest Men in white T-shirts with poles are pictured in Yuen Long. Photograph: Tyrone Siu/Reuters

Organisers said they had mapped out the safest route possible along main roads, from a playground in the centre of the district to the railway station where the attack took place.

The violence in Yuen Long marks a sinister turn for the demonstrations, which had been largely peaceful.

Hailey Leung, a university student who has been attending the protests this summer, said: “The fear of the gangs is definitely stronger than the fear of the use of violence of the police.”

Her parents have been supportive of the protests but, since the violence in Yuen Long, they have asked her not to attend.

“I believe some if not most of the young people will continue to fight for what they want, even if they know it is going to be dangerous,” she said. But Leung may not attend the rally on Saturday, saying: “It is one thing to run away from teargas and another thing to fight against the gangsters.”