The police may arrest a person according to a warrant issued by a Magistrate under Sections 31, 72, 73 or 74 of the Magistrates Ordinance (Chapter 227). For example, an arrest warrant may be issued if an accused person does not appear in Court when he is due to answer a charge.
However, an arrest warrant is not always necessary. Under Section 50(1) of the Police Force Ordinance (Chapter 232), a police officer can "apprehend" (i.e. arrest) a person if he/she reasonably suspects the person being arrested is guilty of an offence. It is not necessary that the officer knows the exact statutory provision that the suspect has violated, so long as the officer reasonably suspects that the suspect has done something amounting to an offence.
Under Section 101A of the Criminal Procedure Ordinance (Chapter 221), any person effecting an arrest may use such force as is reasonable. A police officer may, for example, employ handcuffs or other means of restraint where it is necessary to prevent escape. Section 50(2) of the Police Force Ordinance (Chapter 232) also allows the police officer to use all means necessary to effect an arrest if the suspect forcibly resists or attempts to evade the arrest.