Reinforcements called as 'dynamic' fire threatens homes

Hundreds of firefighters are battling a blaze that may threaten communities after burning through thousands of hectares.

Interstate reinforcements have arrived to help contain the fire at South Australia's Deep Creek south of Adelaide that has destroyed structures and burnt 3700 hectares.

"If the containment lines are not effective, the predicted spread of this fire has the potential to reach surrounding communities," a South Australia Country Fire Service statement said on Friday.

Residents at the Fleurieu Peninsula's Rapid Bay, Second Valley and Yankalilla are on high alert after crews fighting the "dynamic" fire were hampered by steep, inaccessible terrain and strong winds.

Almost 300 firefighters are battling the blaze after backup arrived from Victoria and NSW, with more set to come from Western Australia on Saturday.

They have been backed by 35 trucks and a further 11 support vehicles working to keep the fire behind containment lines.

Water bombers have also provided support from the air, completing almost 1000 drops in the area to date.

The number of structures destroyed by the fire that has raged for days rose to seven on Friday, and there was believed to be significant wildlife loss.

A community meeting was held on Friday at Yankalilla to warn locals about the ongoing fire threat.

Incident Controller Cameron Leary urged local communities to be ready to enact their bushfire survival plans.

"If you get a message that says you need to take action, instigate that plan, take that action and do it early," he said at the meeting.

"If it's to leave, and you get a messages saying you could come under threat, then leave.

"If it's to stay and defend, then enact your plan to stay and defend, but do not vary from the plan you have made - you need to make a decision."

Mr Leary said the arrival of WA firefighters on Saturday would provide welcome support and timely relief for exhausted locals.

"Hopefully with these resources we can allow some of the local people who have been out there to take a break and have a rest," he said.

Members of the public were urged to refrain from flying drones in the area, due to the risk posed to firefighting aircraft.

Three drones had forced the grounding of aircraft in other recent fires, Mr Leary said.

"If we have a drone in or around our fire grounds, our aviation wing has to stop until that drone is removed," he said.

The cause of the Deep Creek fire was yet to be determined, but was not believed to be suspicious.