The grassfires were lit between 2.20 and 7.20pm between Two Wells and Dubin north of Adelaide yesterday.
“Country Fire Service (CFS) crews were able to bring all fires under control quickly with minimal damage, however the potential risk to local communities was significant given the weather conditions,” SA Police said in a statement.
Police are investigating the incident and patrolled the areas overnight.
All blazes are now controlled.
A cool change has hit the state today, with showers and a top of 24 degrees expected for Adelaide.
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It comes as the CFS fought blazes in Port Lincoln and the Eyre Peninsula during the week.
Temperatures remained in the 30s on Thursday night and early Friday morning.
Kingscote, a town on Kangaroo Island, had its hottest minimum temperature in 16 years, only dropping down to an overnight low of 24.9 degrees.
Residents of Kangaroo Flat were issued emergency warning messages to take cover from a blazing bushfire, which was started by the heat, while water-bombing helicopters were called in to help extinguish the blaze.