Australian firefighters continued to battle the devastating Adelaide Hills bushfire on Christmas Day.

Slightly milder conditions on Wednesday and on Boxing Day will give the state's Country Fire Service a chance at bringing the 25,000-hectare blaze to heel ahead of hot weather forecast for the weekend.

A 'watch and act' warning remained in place for the region, where fires have destroyed 84 homes and hundreds of other buildings as well as claimed one life.

A return to very hot weather has been forecast for the weekend, with temperatures set to top 40C together with rising winds.

Members of the Salvation Army and volunteers helped prepare a Christmas lunch for the firefighters before they headed back out to fight fires.

"It'll be an opportunity for us to just help them remember that it is Christmas Day," said Alan Steven of the Salvation Army.

Country Fire Service Chief Mark Jones said he was inspired by the efforts of his volunteers who continue to work to bring the fire under control.