Crimes Act 1914

Arrest without warrant of offenders against this Part  
83B
A person may, without warrant, arrest another person:

(a) if that other person has committed, is committing, has attempted to commit or is attempting to commit an offence against this Part;

(b) if there is immediate danger that that other person will commit or attempt to commit an offence against this Part; or

(c) if that first-mentioned person is a constable and he has reasonable grounds for suspecting that that other person has committed, is committing, has attempted to commit, is attempting to commit or is about to commit an offence against this Part;

and the arrested person may be detained in proper custody to be dealt with according to law.