"Fire and Emergency urgently urges people to stay away from the Scroggs Hill Rd area."
People in the area trying to get a look at the blaze have been a "barrier" to getting resources to the site, it said.
There are three helicopters and 30 firefighters currently working on the fire, it said.
A post to the Fenz Communication Centres Facebook page said: "Fire crews from Brighton Volunteers, St Kilda, Dunedin City, Lookout Point, Mosgiel ... and the rural resources from Four Wakari crews are battling to contain and extinguish the blaze."