National security police on Tuesday arrested two men on suspicion of violating the sedition law.
The pair, aged 28 and 29, are alleged to have published posts promoting ill-will and enmity between different classes of Hong Kong people in a social media group they are said to have managed.
Sources said the suspects work in the Home Affairs Department and the Office of the Government Chief Information Officer and that they are the administrators of the Facebook page "Civil Servants Secrets".
In a statement, police said officers also investigated five other men, two of whom were arrested for fraud.
The sources said they are ambulance personnel under the Fire Services Department, and were allegedly involved with posts on the Facebook page.
The force said officers searched the offices and homes of the seven men with a court warrant, and seized some communication devices.
The four suspects arrested are being held in detention, with officers saying further arrests could be made as their investigation continues.