The four fires, between midnight and noon yesterday, destroyed two sheds and damaged property at two other addresses.
The first fire happened shortly before 12.10am in Severn St. A hay shed was destroyed after being set alight.
Fire crews were called back to the shed about 10.50am to dampen down the smouldering remains of the building.
The second fire, about 3.30am, gutted a storage shed on the Bluff Highway.
The third fire was at a Bain St house.
The sleeping occupants were alerted by neighbours who had noticed the fire in property lying against the outside of the house.
A disused refrigeration unit on the roof of a hat shop in the South City Mall in Elles Rd was set on fire between 6am and 9am.
Detective Fred Shandley, of Invercargill, said it was too early to comment if the fires were linked.
Investigations were continuing.
