A Hong Kong university ordered its student union to shut down after a message was posted on campus expressing condolences and urging justice for the victims of a major fire, according to a letter publicly shared on Friday.

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) said it will "suspend the operations" of the student union acting executive committee with immediate effect and take over their facilities, according to a letter shared on social media by the union on Friday.

The school cited reasons such as a lack of representation and poor financial management, which the union called "unfounded and arbitrary".

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

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 multiple requests for comment from AFP.

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.