CANBERRA -- Firefighters in South Australia (SA) are continuing to fight a bushfire that poses a significant threat to several towns.

More than 300 firefighters spent Sunday night battling the blaze that started at approximately 4:00 pm local time on Sunday near the town of Cherry Gardens in the Adelaide Hills.

The fire was downgraded from "emergency" level to "watch and act" but remains a significant threat.

Temperatures exceeding 40 degrees centigrade across the state on Sunday were exacerbated by strong winds, creating the most dangerous bushfire conditions of the season so far.

Several buildings have reportedly been damaged but the blaze has been prevented from reaching towns in the region.

Firefighters on the ground were initially assisted by water bombing aircraft that were grounded as light faded.

Yvette Dowling, the Country Fire Service (CFS) Deputy State Commander, said that the fire was "significant" but that changing conditions including forecast rain and reduced wind would help firefighters.

"The most significant fire is the Cherry Gardens fire," she said.

"It's going to be very difficult to control."

South Australian police on Sunday said that they have arrested a man suspected of causing a separate fire in the Adelaide Hills.

They said that the man, aged in his 60s, was caught speeding away from the scene of a fire at Clarendon, 10 km south of Cherry Gardens, at 6:00 pm local time.

The fire was extinguished by members of the public after causing minimal damage.

Police are investigating if there are links between the Clarendon fire and others they suspect were lit intentionally.