Hong Kong police charged a student leader from the Baptist University of Hong Kong with possession of offensive weapons on Tuesday after they found 10 laser pointers in his bag as he walking through Sham Shui Po in Kowloon.

Police said the items were not “laser pointers” but “laser guns” and held a demonstration during a press conference on Wednesday. They pointed the beam from a “laser gun” at a piece of newspaper two meters away for about 10 seconds and then smoke started coming from the page and a burned spot formed on the newspaper page.

Police condemned the protesters for using “laser guns” to target their officers, saying protesters pointed at their officers’ eyes at previous protests and could have caused injuries.

The arrest led to another night of clashes and crowd dispersion and police fired tear gas at people gathered outside the district police station who were demanding the release of the student leader.

Keith Fong Ka-shing, the 20-year-old president of the Baptist University’s Student Union, was intercepted by police on Apliu Street in Sham Shui Po on Tuesday evening.

Video footage showed four plainclothes officers, all in black T-shirts, surrounding Fong and shouting at him, accusing him of trying to run away when they approached him.

Fong said he tried to run because he did not know who the men were. He repeatedly asked the officers why he was being held.

The officers then searched his bag and found 10 laser pointers in a plastic bag. Fong said he bought the pointers for star-gazing – a meteor shower is due to happen on Friday.

Fong was later told he was arrested for alleged possession of offensive weapons. The crowd who witnessed the arrest surrounded Fong and were angry with the officers when they heard the accusation. The crowd demanded the officers release Fong.

After his arrest, Fong said he was feeling unwell and vomited. He was sent to Caritas Medical Centre. It was understood Fong has asthma.

Ronald Chin, the vice-chancellor of the university, went to the hospital to see Fong. Speaking to reporters afterwards, he quoted Fong as saying an officer grabbed him by the throat while he was in the ambulance, Radio Television Hong Kong reported.

A few hundred protesters went to Sham Shui Po when news of Fong’s arrest spread on social media. They surrounded the Sham Shui Po Police Station and called for his immediate release.

Some of the demonstrators daubed graffiti on the building’s walls, while others shone lasers at the officers inside.

At about 11.20pm, police fired tear gas from inside the station at the crowd on Yen Chow Street. Riot police were deployed to the area and pushed the protesters down toward Apliu Street.

Seven men and two women were arrested, including a Shatin district councilor, and the protesters left after midnight.

Li Kwai-hai, a senior superintendent at the organized crime and triad bureau, said the plainclothes officers were off duty and discovered the student bought the 10 lasers for HK$4,250 (US$542) at a stall in Sham Shui Po.

Li justified the arrest by saying Fong acted suspiciously when the officers approached him. They found 10 18-centimeter-long laser pointers in a bag and added that anyone in possession of them could be classified as carrying “offensive weapons.”

The police were criticized over what some said was an abuse of power by arresting a person with laser pointers. James To, a lawmaker from the Democratic Party who is also a lawyer, said that unless a person is carrying a weapon such as a knife, police cannot justify an arrest based merely on their suspicions.

The laser pointers cannot be classified as an offensive weapon, said To. The multiple numbers of them found also concludes nothing, he said. To said he was sure that police were abusing their power.