More than 1000 emergency calls were made to authorities on Wednesday as strong winds fanned the bushfire through the Natone Hill reserve at Lindisfarne, with the blaze licking the back fences of homes.
It burned about 25 hectares and took three hours to bring under control.
Tasmania Fire Service spokesman Stuart Males said on Thursday that investigations determined the fire was deliberately lit.
"We have witness statements from people in the area who have given us some information which has been passed on to police," he said.
Detectives subsequently said they are seeking two boys, aged about 15, who were seen in the area at the time, one of whom was pushing a bicycle.
Smoke had cleared on Thursday morning to reveal a large tract of charred ground.
"It did creep down toward fence lines at the back of properties," Mr Males said, adding specialist crews remained on stand-by.
A total fire ban was in place for southern Tasmania on Wednesday and the senior officer said such deliberate acts were frustrating.
"The temperature, the humidity and the wind all came together to create the right conditions for a fire that (could) have major impacts to a populated area, Mr Males said.
"To have something like that occur late in the day when those weather conditions were going to continue until around 9pm, it certainly puts a strain on the resources.
"If it had been a rural area with our resources being further away, it would have been a different scenario - it certainly had the potential to make a severe run over a long stretch of ground and the consequences would have been different."
There were no injuries or reports of property damage.
Crews are expected to remain at the scene for the next few days.
© AAP 2017