The man got back on his bicycle and rode off down Maidstone Rd towards Avonhead.
A member of the public followed him in their car and saw him ride into a cul-de-sac street nearby.
Police are yet to speak with this witness and encourage them to ring Canterbury Police on 03 363 7400 immediately.
Police went to the address, and located a man who is now in custody.
Worner said he would like to thank the person who stopped to help the second victim and asked that anyone who saw either event to call the Christchurch Police on 03 363 7400.
"We ask these people to contact us right away, their assistance this morning has been invaluable," he said.
"It's important to remember that people should be alert, not alarmed following these incidents.
"As the alleged offender is talking to police we are confident the public has no reason to be concerned."