They arrived at the Composite Building around 3pm on Friday. They searched the students' union office, the office of the union council, as well as the offices for Campus TV and publication Undergrad.
Officers also spoke to the editor-in-chief and the deputy editor of Undergrad. They were released after the questioning.
Samson Tse Shu-ki, the dean of student affairs, arrived at the scene to offer help as well. He added the students spoke to a lawyer and was taken care of.
However he refused to disclose more information regarding incident.
Police, with a Court Order, entered the campus the investigate a case, the university confirmed in the afternoon.
Sources said that the case was triggered by a suspected breach of article 27 of the national security law, involving advocating terrorism or inciting the commission of a terrorist activity.
Earlier the students' union passed a motion that voiced appreciation to the attacker in Causeway Bay. It soon retracted the motion and apologized for it. Yet it still drew fire from the school and different government sectors.
Hotter, sunnier and wetter. Britain's weather in the last 30 years was different to the preceding three decades.