Police are not including a fire in a doorway of a building at St Columba's Church, Taradale, on Easter Sunday.
It is not believed to be linked to the Hastings incidents, and also at this stage they are not linking a small number of fires in Totara St, Hastings in February.
But Hawke's Bay area CIB investigations officer-in-charge Detective Senior Sergeant Martin James is sure the fires in Hastings since the end of February are linked.
"We are quite confident.
"And we are sure there are people who know the information we need.
"We need that call, immediately.
"There are not a lot of people on the streets at that sort of time," he said.
"If it's half-past-two in the morning, and there are people out on the street, they're possibly up to no good.
"Anyone walking the streets around the Grove Rd, Sylvan Rd and St Aubyn St area in particular."
In one of the arsons, a car in Jellicoe St was torched after an intruder flicking a cigarette lighter was disturbed in a house occupied by a woman and her children.
The Miller Street fire followed soon afterwards.
Anyone with information should phone Hastings police on 06 873 0500 or Crimestoppers on 0800 555 111.
Heat trail
•Saturday, February 28, midnight: Relocated vacant house on a vacant section in Victoria St was set on fire
•Sunday, March 1: Fire destroys a relocated property on Hastings St.
•Friday, March 13, 5am: Vehicle set on fire outside a Jellicoe St house.
•Saturday, March 14, 4.25am: Car parked on Alexandra St set on fire.
•Saturday, March 14, 5.56am: Vacant house in Miller St set on fire, extensively damaged.
•Wednesday, April 1, 12.30am: Classroom at St John's College was set on fire.
•Wednesday, April 1, 2.03am: Truck set on fire in driveway of Buller St address.
•Sunday, April 5, 6am: Pirate ship at Splash Planet set on fire and destroyed.