Large numbers of police were on the streets of Hong Kong on Saturday night as officers conducted stop and searches on public transit lines and questioned residents wearing black, the colour adopted by protesters, after a mass rally dispersed to mark the fifth anniversary of the pro-democracy “umbrella movement”.

Protesters changed into civilian clothes in alleys and behind walls of umbrellas in districts close to government headquarters, where earlier police fired a water cannon filled with dye and abrasive liquid from behind defensive barriers.

Play Video 1:10 Teargas and water cannon fired at Hong Kong protesters – video

Officers in defensive clothing filled Harcourt Road and a highway overpass in front of the government complex hundreds of metres deep as protesters on the frontlines threw rocks at windows and over police barriers.

Before the water cannon was fired, a small band of masked protesters lit a flag of the Chinese Communist party on fire, shouting “fuck Communists” and “fight for freedom!” to cheers from nearby crowds.

The gathering, however, lasted less than two hours as tactical police arrived on the scene, forcing protesters to flee over road barriers to avoid arrest before larger demonstrations planned for the rest of the week.

Some said they would head to Mong Kok police station on the Kowloon peninsula, where protesters have regularly gathered in small numbers to shine lasers and shout at police.

Major demonstrations, however, appeared to be over for the night as protesters disappeared into the winding side streets of the historic Central and Sheung Wan districts even as two subway stations on Hong Kong island were closed.

Earlier, thousands of peaceful protesters filled Tamar Park on the other side of the government complex to remember the umbrella movement that paralysed Hong Kong for 79 days in 2014, forming the basis for the current protest movement that has roiled the city for the past four months.

Before the police-sanctioned rally began in Tamar Park, next to the government buildings, officers raised a red warning flag and fired pepper spray on protesters, who were shining lasers and banging on the gates of the central government building. Protesters dispersed and occupied an adjacent major road.

The police said “violent protesters” had damaged property and aimed laser beams at a helicopter, “posing a serious threat to the safety of everyone at the scene”.

Facebook Twitter Pinterest People shine laser beams at a rally in the Admiralty area of Hong Kong. Photograph: Philip Fong/AFP/Getty Images

Later, police used teargas and a water cannon, which sprayed pepper-laced blue dye over protesters who had been throwing rocks over the barrier, shattering windows on the lower level of the government headquarters. They also threw petrol bombs at police.

Hong Kong was braced for consecutive days of protests and probable clashes, culminating with anti-government demonstrations on Tuesday to coincide with China’s National Day, a politically important anniversary marking 70 years since the founding of the People’s Republic of China.

Hong Kong’s legislature put out a “red alert”, evacuating staff and politicians from the legislative complex, which protesters have previously broken into. Dozens of riot police vans were parked nearby, and water barriers protected the government building.

Protesters clad in black, with gas masks and helmets, were also preparing for clashes. “The Hong Kong police are attacking our protesters and the force is unnecessary,” said a 22-year-old man, who planned to be on the frontline of protests to try to protect other demonstrators. He asked not to give his name for fear of arrest.

“What we really want is not to fight with police; all we want is to protect the people who are peaceful so they can safely leave,” he said.

Earlier on Saturday, protesters hung banners and plastered posters outside the complex, building a “Lennon wall,” named after the John Lennon Wall in Prague, for political graffiti and messages. A group of masked musicians and singers performed the song Glory to Hong Kong, which has become the protesters’ anthem.

Facebook Twitter Pinterest People look at posters on the ‘Lennon wall’. Photograph: Billy HC Kwok/Getty Images

The Lennon wall stretched around the government complex, where it was originally started in 2014. Demonstrators hung large banners in yellow, the colour of the Umbrella movement, with the words: “We are back.”

The protests, which began in June over an extradition bill, have now lasted longer than the Umbrella movement and have expanded both in scope and tactics. The mostly non-violent 2014 protests were concentrated on a major road outside the government buildings.

The recent demonstrations have sprung up across the city under the mantra “Be water” – a quote from the actor Bruce Lee. The protesters’ demands echo those in 2014 – the implementation of genuine universal suffrage – but have also demanded an independent inquiry into police behaviour and reforms to the police force, which has lost considerable public trust.

The protests have often turned violent, with police firing thousands of rounds of teargas and pepper spray on protesters, as well as deploying water cannon. Protesters have also increasingly been physically attacking critics and people they accuse of being “mainland spies”.

Facebook Twitter Pinterest A woman who was beaten after removing anti-government posters is treated by medics. Photograph: Nicolas Asfouri/AFP/Getty Images

As thousands rallied on Friday against the government’s use of a controversial holding centre, a woman was kicked, punched and spray-painted for tearing down posters. Other protesters tried to protect the woman and treat a head wound as the attack continued.

“These people started beating me up for no reason,” she said, declining to give her name. She acknowledged she had torn down the protesters’ posters but criticised them for not allowing her to express her views.

“It doesn’t mean that people with different political views should be beaten up,” she said. “If you encourage democracy, freedom of speech, this is not the way that people should do [it].”

Despite the violence, the protesters maintain broad public support. “If I were 50 years younger, I would be out there at the front with them,” said Ng Yin Fai, 72, who has been joining the protests since June. “If we don’t protest today, we won’t have this chance again.”

Play Video 5:02 Uncle Wong, 82: protecting Hong Kong protesters with his walking stick – video

On Saturday a US academic who testified in a congressional hearing alongside democracy activists last week was denied entry to Hong Kong. Dan Garrett said officials told him he could not enter because of “unspecified immigration reasons”.

A government spokesman, responding to protesters’ calls for universal suffrage, said “one man, one vote”was the ultimate goal, as enshrined in Hong Kong’s constitution.

“To achieve this aim, the community needs to engage in dialogues, premised on the legal basis and under a peaceful atmosphere with mutual trust, with a view to narrowing differences and attaining a consensus agreeable to all sides,” the government said in a statement.

Residents said that while they were scared of potential arrest or violence from the police, they would continue to protest. “Some of us may feel scared deep inside when we see the police. We feel scared by being simply young or just wearing black,” said Yen, a secretary in her 30s, as she glued black paper stars with the words “Liberate Hong Kong” on to a pavement.

She said China’s influence over Hong Kong had grown since the Umbrella movement ended, with the press and freedom of expression being stifled and pro-democracy activists being charged and jailed.

“Just being frightened is not an excuse for us, because we have no way back,” she said. “We can’t go back to our normal state where China is taking over.”

Additional reporting by Laurel Chor