The office of an assistant professor who relocated from Singapore for a post at City University of Hong Kong has been vandalised and spray-painted with pro-democracy slogans after he told students not to bring their political agendas into the classroom.

Tan Yong Chin, who lectures in marketing at CityU, had issued a warning in an email that was later circulated in online chat groups.

“For any future presentations in class, if you use it as an opportunity to broadcast any political announcements or statements, the whole group will automatically get zero points for the presentation,” he wrote on Friday.

CityU students responded by spraying derogatory graffiti on the front of his office, including the words “white terror” and “Hongkongers rebel”.

One wrote: “You are here to teach. Do not bring your political agenda into assessment criteria.”

Hong Kong students have responded aggressively when met with attempts to quell pro-democracy demonstrations that have roiled the city since June. The unrest, initially triggered by a controversial proposed change to extradition law, has even spread to local secondary schools.

Earlier this month chaos erupted at the Chinese University of Hong Kong when more than 100 students stormed a faculty building demanding to speak with the vice-chancellor over his alleged lack of support for students who had been arrested during protests.

The distrust of authorities has sparked vandalism both on university campuses and in the streets. Radical protesters have trashed and burned shops, bank branches and subway stations, with some even assaulting bystanders voicing opposition to their actions.

Last week the Hong Kong Design Institute cancelled all classes for three days after dozens of masked students smashed glass doors and security cameras on its campus over the school’s refusal to release surveillance footage of a 15-year-old student found dead. Her body was recovered from the sea on September 22, and she was said to have attended anti-government protests regularly. Police said an investigation had found nothing suspicious about her death.

View photos An anti-government protester starts a fire in Mong Kok. Photo: May Tse More

CityU’s student union said it had asked the university management to strike down Tan’s threat to award a mark of zero, according to Singapore’s Chinese-language newspaper Shin Min Daily News.

But a spokesman for the institution told the paper the school was not aware of the professor’s comments and would look into the matter. He added that teaching materials must be related to the content of a course.

This Week in Asia understands that Tan has since closed his social media profiles.

Tan on Wednesday said the university has been “very supportive”, and has made arrangements to ensure his safety. “The university has set up a task force to look into this issue, and I trust that they will make a decision in the best interest of all students.”

Tan also clarified that the email to students last week “had nothing to do with the Pooh image or Vans campaign”.

He was referring to earlier statements online claiming that Tan was discontented with images of Winnie The Pooh that were presented by students in his class. Images of Winnie The Pooh are censored in China as netizens often drew parallels between the character and Chinese President Xi Jinping.

Earlier allegations also claimed that students had made protest-related presentation slides, which included Chinese tea shop chain Hey Tea and American streetwear brand Vans.

Anti-government protesters had earlier called for a boycott of the sneaker brand after it removed entries from its annual Custom Culture sneaker design contest that alluded to the unrest in the city sparked by a now-withdrawn extradition bill.

“I hope everyone can look beyond that email and understand my intention, which is to create a safe and conducive learning environment where students can focus on content that is relevant to the course,” Tan said.