More than 135 fires were burning in NSW on Tuesday night, threatening homes and injuring firefighters as regional communities bore the brunt of the ''catastrophic'' conditions of 40-plus temperatures and high winds that emergency services had warned about.

The fires claimed their first home last night - one property was confirmed to have been lost at Jugiong near the NSW-ACT border.

Power to almost 10,000 homes in Sydney, the central coast and the Southern Highlands was also cut for a time, because of widespread equipment failures.

One of the NSW fires temporarily cut the Hume Highway at Tarcutta about halfway between Melbourne and Sydney.

As night fell, the worst fires continued to burn in southern parts of the state, around Bega, Cooma, Wagga Wagga and Nowra in the Shoalhaven region. The Hume reopened late in the evening as the direct threat to Cooma abated.

By late Tuesday night, more than 60,000 hectares had been razed across the state but there were no reports of loss of life.

Rural Fire Service Commissioner Shane Fitzsimmons praised the ''extraordinary'' effort of the 1600 firefighters in the field that was taking place in NSW in ''dirty, hot difficult conditions''.

Mr Fitzsimmons said a large amount of damage had been done to infrastructure in pasture country across the state, with 1000 head of stock lost.

''We've still got many hours of very difficult conditions being faced for NSW. That's tonight alone, let alone looking into tomorrow,'' he told ABC television.

''Particularly as this southerly change moves northward, we can expect some fairly intense and erratic weather behaviour,'' he said.

Opposition Leader Tony Abbott was among those waiting to help if a fire broke out in bush in Sydney's north, joining his local fire brigade where he volunteers.

Sydney recorded a peak temperature of 42.5 degrees.

By early evening, the biggest threat was at Deans Gap, in the Shoalhaven region, where fires were fuelled by strong, hot wind gusts.

The fire at Tarcutta, near Wagga Wagga, burned through hundreds of hectares of land, isolating residents in properties to the north-west.

They were warned to stay and protect themselves from radiant heat because it was too late to leave.

Police in western Sydney arrested three juveniles over what they believed was a deliberately lit fire in Shalvey, in the west. Up to 15 fire crews and five police cars battled for two-and-a-half hours to bring the blaze under control, with 10 hectares affected.

All NSW national parks, reserves and state forests were closed to the public due to the fire risk, while the total fire ban has been extended into Wednesday.

A man was charged for breaching the total fire ban in the Illawarra region after he allegedly lit a cooking fire, and tried to prevent police from extinguishing it as hot ash fell to the ground.

The 70-year-old property owner is due to appear at Port Kembla Local Court on April 4.