PERTH, Australia — Firefighters battling wildfires in Australia’s most populous state attempted to make headway Thursday amid favorable conditions, before an "extreme heat wave" hits embattled areas on the weekend.

Thousands of firefighters in New South Wales took advantage of cooler weather and continued to strengthen containment lines. More than 70 fires, however, were still burning across the state with areas in the south coast currently at the “watch and act” level issued by fire services.

About 12.35 million acres of land have burned nationwide over the past few months, with nine people killed and more than 950 homes destroyed. New South Wales has received the brunt of the damage, with around 850 homes razed in the state.

Authorities are bracing for conditions to deteriorate as high temperatures return. Sydney is forecast to hit 31 degrees Celsius (88 Fahrenheit) on Sunday before reaching 35 C (95 F) on Tuesday. The city’s western suburbs could reach 41 C (106 F) on Sunday.

Bureau of Meteorology forecaster Rose Barr said a heat wave was currently building in southern parts of New South Wales before worsening on the weekend.

"Some areas are forecast to reach extreme heat wave conditions,” she said. "With the increasing heat and winds, the fire danger will worsen into the new week, with Monday and Tuesday most likely to be the most significant fire weather days.”

Fire danger ratings remained very high in northwestern New South Wales, and high in Sydney.

Meanwhile, South Australian firefighters Thursday were battling wildfires in Adelaide Hills, which has been downgraded to the “advice” level.

South Australia state last week had 86 homes destroyed after wildfires flared in catastrophic conditions. A return of extreme temperatures, however, are expected with Adelaide, the state capital, set to reach a sizzling 40 C (104 F) on Friday to start a four-day heatwave — its second such hot spell in just over a week.