It took the Fire Service more than hour to extinguish one of the fires.
Detective Sergeant Brett Roberts said while it was difficult to connect all the fires, eight took place in a similar area over a similar time period, and one - in a trailer loaded with rubbish in Jellicoe Cres early yesterday - might be related to a series of nine small suspicious fires in Kaikorai Valley the previous weekend.
He said the latest series of fires were mostly early on Saturday, with four beside the Southern Motorway at Saddle Hill, two in Fairfield, one in South Rd and one in Burns St, all reported between midnight and 1am.
The fires were all in vegetation, which was particularly concerning because the area was windy and very dry, and fire could easily take hold and spread to nearby houses, he said.
Two police officers had seen a couple of the fires in their early stages, but were unable to put them out with extinguishers because they took hold very quickly, he said.
"They appear to be caused by mindless idiots, probably in cars, driving along and somehow starting these fires as they go.
"We know that in those areas, there would have been people out who saw something - laughter, talking, a car squealing off.
"We are only going to be able to solve this with the assistance of the public."
Anyone who had any information or who heard or saw anything unusual on Friday night or Saturday morning, or around the time of the Jellicoe Cres fire about 2.45am yesterday, should call their nearest police station or report it anonymously to the Crimestoppers line on 0800 555 111.
