At least seven firefighters were injured battling an out-of-control blaze at Sampson Flat in the state's Mt Lofty Ranges.
Residents of 19 communities were asked to evacuate as a predicted shift in the winds yesterday afternoon prompted fears the flames could worsen.
The forecast was also for increased humidity, which could slow the fire's progress, Hamilton said.
Up to 2000 firefighters were battling the blazes across the state from the ground and the air, with more than a dozen aircraft dumping water on to the flames.
Four firefighters suffered minor physical ailments, including dehydration and asthma, Hamilton said.
In neighbouring Victoria state, firefighters have controlled more than 300 fires since Friday, with only one still considered a danger.
One home was destroyed in the blaze in the western Victoria town of Moyston, state Country Fire Service spokesman Mario Xuereb said.
A shift in the weather late yesterday was expected to bring light rain, wind and lightning to the area, which could exacerbate the blaze.
The rain wouldn't be enough to quell the flames, and the lightning could spark fresh fires, Xuereb said.
The Mt Lofty ranges scrub fire was yesterday travelling erratically and burning freely in all directions.
The Country Fire Service says lives are at risk in towns including Upper Hermitage, Chain of Ponds and the townships of Inglewood, Houghton, Cudlee Creek, Lower Hermitage, Forreston, Lobethal, Mount Torrens, Charleston, Williamstown, Woodside, Lenswood and Mt Pleasant.
"One of our appliances was caught by the fire and several people have injuries," CFS spokesman Rob Sandford told ABC radio.
"We don't know the full extent ... [but] they are being treated and supported by SA Ambulance."
Country Fire Service chief officer Greg Nettleton said the Sampson Flat fire had burned through about 10,000ha of scrub.
Lightning had sparked new fires, causing further headaches for firefighters already working in tough conditions.
Nettleton confirmed that six CFS volunteers had been injured fighting the blaze, most of them suffering smoke inhalation.
In South Australia, firefighters were "all working in very arduous conditions and doing very, very hard work," Sandford said.
"They're doing their absolute best in what are the worst of conditions imaginable for firefighting.
"We just want them all to come home safe, because this situation is very dynamic and we don't want the tragedy of any of our firefighters being injured or worse."
In 2009, wildfires killed 173 people and destroyed more than 2000 homes in Victoria.
- AAP, AP
