Forty firemen from Kaitangata, Balclutha, Milton and Owaka plus four fire appliances and five water tankers were joined by forestry workers from Wenita Forestry and City Forests in the battle to stop the blaze spreading into neighbouring forestry blocks and Department of Conservation land.
Wenita Forests forest products spokesman John Kerr said the fires started about 1km apart, and he believed they were deliberately lit.
"The chances of having two fires in the one location of that size, it certainly couldn't have sent a spark down the road.
"The only reason the second fire was picked up was because we were in the helicopter with night-vision goggles, and it was easy to spot from the air."
The Kaitangata volunteer fire service was called to the fire just after midnight, and chief fire officer Kevin Sutton said he also believed the fires were started deliberately.
"The [main] fire was contained in a five- or six-hectare area, but had the potential of being heaps [bigger].
"Fighting a bush fire can be more dangerous than fighting a house fire, with the winds changing," he said.
"Once again, this is putting us at risk."
Mr Sutton said it was lucky the fire did not get into the big trees and there was little wind.
"It's going to take days to put this out."
Michael Abbott, of Abbott Contracting Ltd, left Mt Allan at 1.45am to help fight the fire.
"When we found out it was a Wenita forest, we needed to get down here pronto.
"I had four guys at Mt Allan who knocked off at 5.30pm yesterday. I had to call them at 2am and get them back. We were down here by 3.30am, and it's all go."
Yesterday, crews were dampening down hot spots and digging over the burnt ground to stop it flaring.
Mr Kerr said Wenita would send people back for a night shift because the fire had not been sufficiently quelled.
Detective Sergeant Kate Bartlett said police were investigating the cause of the fires.
