More than 70 fires are raging across the state, 41 of them uncontained.

The NSW Rural Fire Service has elevated more than 10 fires to "emergency" warning level - three across northern NSW, one near Coffs Harbour, one in the Hunter, two near Kempsey and a cluster near Taree in the mid-north.

A blaze at Thunderbolts Way in Bretti, northwest of Taree, is burning out of control across 10,000 hectares, while other fires are burning unrestrained at nearby Hillville, Rumba Dump and Mares Run.

There are also emergency fires farther north at Washpool State Forest in Coombadjha, at Bora Ridge near Evans Head and Torrington north of Glen Innes. The latter has razed 60,000ha.

The other three fires affect Carrai East in Willi Willi National Park, a 75,000ha tract northwest of Port Macquarie, Liberation Trail near Coffs Harbour and Buckra Bendinni near Nambucca Heads.

A fire on Wine Country Drive in North Rothbury, near Cessnock, was also on Tuesday afternoon lifted to "emergency" level.

At Llangothlin near Armidale, a 1500ha fire has been downgraded from emergency to "watch and act" level.

"The reality is conditions will simply continue to get worse and deteriorate over the coming hours and particularly into this afternoon" driven by rising temperatures and high, dry winds," RFS commissioner Shane Fitzsimmons told reporters in Sydney.

Mr Fitzsimmons said the day was unfolding as predicted with a million hectares burning. He said two homes were feared destroyed at Hillville but there had yet been no reports of civilian or firefighter injuries.

NSW is dealing with unprecedented fires during what NSW Emergency Services Minister David Elliott says could prove the most dangerous bushfire week in Australia's history.

More than 3000 firefighters and 80 aircraft will potentially be involved in battling blazes.

Premier Gladys Berejiklian urged residents to heed warnings and head for safety.

"We need to make sure every community member takes the opportunity to assess the situation and act with precaution in every possible manner," she said.

A catastrophic fire danger rating - the highest possible - is current for the Greater Sydney, Greater Hunter and Illawarra-Shoalhaven regions.

Temperatures in the high 30s, low humidity and winds gusts beyond 70km/h coupled with drought mean the state faces "horrendous conditions", the RFS said.

People in the path of fires are being urged to relocate, with the warning specifically directed at residents proximate to a blaze in the Wollemi National Park north of Sydney.

"If you are in the area of Mellong, St Albans and Upper MacDonald and your plan is to leave, leave now to a safer location," the RFS said.

There is also concern regarding a small fire at Llandilo in western Sydney which the RFS deemed out of control.

"Leaving early and well ahead of any fire in your area is the safest option," Mr Fitzsimmons said.

"Safest options might include going to the local shopping centre, going into town, where you're not in the bushfire-prone area."

With embers known to jump 20 to 30 kilometres in front of a catastrophic blaze, firefighters attempted tactical backburning operations on Monday night but Mr Fitzsimmons said their impact would be "tenuous at best".

There are extreme fire danger ratings - the second-highest level - for the north coast, southern ranges, central ranges, New England, northern slopes and northwestern areas.

A week-long state of emergency has been declared in NSW, with Defence standing by to provide support including for search and rescue operations.

Some 600 schools were closed for the day and nine schools were on Tuesday afternoon safely evacuated.

The bushfires, which hit hard on Friday, have claimed three lives and destroyed at least 150 homes.

Australian Associated Press