Bushfires that razed dozens of homes in southeast Australia have now been mostly contained, but not before causing damage to or destroying several homes and other buildings.

The New South Wales Rural Fire Service Commissioner said the worst-hit town was Tathra on the south coast of New South Wales state, where more than 70 homes and businesses were severely damaged or destroyed by a fire that started in woods around midday on Sunday.

Power was cut to thousands more properties, and many livestock were killed.

He added that some of Tathra's evacuated residents would be able to return to their homes on Monday, as emergency workers restore power to the devastated area.

The New South Wales state Premier Gladys Berejiklian told reporters in Sydney that she's "absolutely heartbroken." She says her state government will do all it can to support those affected.

Meanwhile, bushfires also ravaged Victoria. Several homes and sheds have been destroyed, and hundreds of residents have been forced to evacuate their homes, according to local media.

Fires claimed at least 18 homes in the state's south-west, but Premier Daniel Andrews was eager to stress how important it was to recognise there has been no loss of human life. However, thousands of livestock have perished in the blazes.

Andrews toured the area on Monday as fire crews worked to extinguish four significant blazes near Warrnambool. These are the state's worst fires of the season.

The rail line between Geelong and Warrnambool also remains closed, with buses replacing trains.

At one stage up to 40,000 homes were without electricity. Power has now been restored to most houses in the area.

Efforts to contain the fires, which are raging across the state's southwest, were hampered by strong winds gusting up to 140kph.

There have been 160 bush and grass fires since Saturday morning, which have burned through more than 40,000 hectares across the state.

Milder conditions have now arrived, and that has helped the 500 firefighters gain the upper hand on the four largest blazes.