The blaze that ripped through Wang Fuk Court in the city's northern Tai Po district last week killed at least 159 people and was the world's deadliest residential building fire since 1980.

The Hong Kong Baptist University (HKBU) told AFP on Friday that it ordered the student union's acting executive committee to suspend its operations "with immediate effect until further notice".

"Only a small percentage of HKBU students are members of the (union). In addition, the Committee has not demonstrated a willingness to abide by the regulations of the University in areas such as financial management," the school said.

The union rejected the reasons in a statement on social media, calling them "unfounded and arbitrary".

"The university's irrational action raises concerns about potential ulterior motives behind this forced suspension," the union said.

Social media users circulated photos on Tuesday of a message stuck onto a student union-run notice board, nicknamed the "democracy wall", which expressed condolences for those killed in the fire.

The unsigned message continued: "We are Hongkongers. Urge the government to be receptive and respond to public demands so justice can be done."

The wall was blocked off with tall barricades on Wednesday, an AFP reporter saw.

Kevin, a HKBU student who declined to give his surname, told AFP at the time he found the noticeboard message to be "positive" and said it drew attention from students walking by before it was sealed off.

The university did not respond to AFP's questions regarding the democracy wall.

Authorities have warned against crimes that "exploit the tragedy" and have reportedly arrested at least three people for sedition in the fire's aftermath.

Student unions at Hong Kong universities were once hotbeds of political activism and played a role in the city's huge and sometimes violent pro-democracy protests in 2019.

They either shrank their operations or were shut down entirely after Beijing imposed a national security law in Hong Kong a year later, which critics say has curbed dissent.