A teacher and six students who were among 12 people arrested on weapons offences were still in police custody on Tuesday, as Hong Kong’s embattled leader told the city’s education minister to “seriously follow up” on any educators arrested during anti-government protests.

Speaking before attending an Executive Council meeting on Tuesday, Chief Executive Carrie Lam Cheng Yuet-ngor also urged schools to stop their students from taking part in “illegal activities”.

She also expressed concern over the arrest of 2,393 students – about 40 per cent of the more than 6,000 people taken into custody during six months of social unrest.

Lam said those arrested included pupils from more than 300 secondary schools.

“Violence entering into school campus poses safety concerns for schools, parents, and students,” she said. “I have requested the Secretary for Education [Kevin Yeung Yun-hung] to seriously follow up on the teachers who are arrested.”

She called on all schools to stop students from taking part in unlawful protests, and ask them to distance themselves from violent scenes as requested in a letter from Yeung on November 21.

Education sector lawmaker and Professional Teachers’ Union vice-president Ip Kin-yuen worried Lam’s comments would put further pressure on the Education Bureau and schools when handling the cases of arrested teachers.

“I hope each and every case will be handled fairly and justly,” he said.

Ip, who said the union had approached some teachers who were arrested during the protests but most cases were still undergoing legal procedures, also felt the government should shoulder the most responsibility for students taking part in protests.

But Wong Kam-leung, chairman of the Hong Kong Federation of Education Workers, said it was “necessary” for the chief executive to make the comments.

“Parents are worried if their children could still learn in a safe and rational environment at school, or if some teachers are encouraging the students to hit the streets?”

Tai Tak-ching, principal of S.K.H. Tang Shiu Kin Secondary School and head of the Wan Chai District Headmasters’ Conference, said there were clear guidelines for following up with the arrested teachers as he said the schools were “more passive” on handling these cases.

“Even when a teacher gets arrested, as long as one is not yet convicted, schools cannot terminate one’s employment and the most that can be done is to suspend one’s duties.”

“Teachers are supposed to nurture young talents and groom them into future leaders,” he said. “They certainly should make a clear stance against violence, and do all they can to prevent students from continuing with these destructive acts, instead of leading them to do so.”

The Education Bureau said between June and early November they had looked into 106 cases related to teachers’ professional misconduct that were related to the protests. Of the 60 cases in which investigation had been completed, allegations were initially found to be true in about 30 cases. But follow up actions have not yet been decided.

But the bureau said it would not disclose the number of arrested teachers because of ongoing legal proceedings.

It added that it had asked the school where the teacher was arrested in Sheung Shui on Monday to suspend him from his duties to “protect students’ safety”, as it would also “seriously follow up” each and every teacher who has been complained, arrested or convicted.

In the early hours of Monday, police arrested 10 men and two women at a car park in Tin Ping Estate in Sheung Shui, and seized home-made weapons including tubes with studs in them, and cans of petrol. The suspects were aged between 14 and 39, and included a teacher and six students, although a police source said the teacher and students were not from the same schools. It is understood that the teacher is from Hong Chi Morninglight School in Tuen Mun, an aided special school for students with intellectual disability.

Officers believe the suspects gathered at the car park, and planned to set up roadblocks as part of the citywide strike that had been called for later that morning.

Those arrested were taken into custody on suspicion of unlawful assembly and possession of instruments fit for unlawful purpose.

As of 1pm on Tuesday, they were still being held for questioning and none had been charged.

Speaking at a police briefing on Monday, Chief Superintendent Kenneth Kwok Ka-chuen said officers were alarmed by the presence of a teacher among those they arrested.

“Teachers are supposed to nurture young talents and groom them into future leaders,” he said. “They certainly should make a clear stance against violence, and do all they can to prevent students from continuing with these destructive acts, instead of leading them to do so.”

As of Monday, police had arrested 6,022 people aged from 11 to 84 since June, when the social unrest sparked by opposition to the now-withdrawn extradition bill began. Of those, 956 people have been prosecuted.

On Monday, five Hong Kong men, who allegedly planned to station a gunman at a strategic site ahead of last Sunday’s anti-government march and “slaughter” police officers along the protest route, appeared in court.

The defendants charged at Eastern Court were among 11 suspects arrested a day earlier, in what police described as the first protest-related case where a gun had been seized.

During the violent protests, police have fired nearly 16,000 rounds of tear gas, more than 10,000 rubber bullets, about 2,000 beanbag rounds and more than 1,850 sponge-tipped rounds. Two protesters have also been shot with live rounds.

Separately, at Liu Po Shan Memorial College in Tsuen Wan on Monday, parents were warned in a letter that their children could face consequences if they took part in any form of political activities at school, which was issued just hours after dozens of students from the secondary school formed a human chain outside its gate, according to its student concern group. The school has not replied to a Post enquiry by press time.

Last month, the Education Bureau issued a letter to 30 government-run secondary schools reminding students not to carry out political activities – such as human chains and slogan chanting – at schools. Other secondary schools have also been advised to follow similar instructions.