Eight blazes have been set across the city during the past three nights. One destroyed a specialised vehicle for disabled children, which police say was a despicable act.
They say most of the fires have been minor, but affected individuals have still suffered significant financial cost.
The latest three fires were lit between midnight and 3.20am on Wednesday.
They were set at the Esplanade Cafe, a construction site on Ashley Street and in a pile of rubbish on Cook Street.
Detective Jacob Baker says police are vigorously following up some lines of inquiry.