Fifteen fires are burning out of control in NSW with firefighters battling 126 fronts, two days after NSW was hit with heatwave conditions.

The pressure is now on to contain the blazes by Friday when the mercury will again climb.

There are total fire bans on today in the state's north, including Gunnedah, Gwydir, Inverell, Liverpool Plains and Tamworth.

Bans are also in place in the North Western region encapsulating Moree Plains, Narrabri, Walgett and Warrumbungle.


Conditions in the areas are expected to be hot with low humidity.

Rural Fire Service (RFS) Commissioner Shane Fitzsimmons urged people to stay plugged into social media and regularly check the RFS website, as well as watch for TV updates.

"People need to be very vigilant, they need to remain vigilant and they need to remain informed and stay alert," he said on this morning.

"We've still got very high or above fire conditions in our northern areas of NSW."

Comm Fitzsimmons said many communities were yet to face the worst.

"We've got 126 fires still, with 15 of those yet to be contained - a lot of work for firefighters. A lot of work for communities affected by these areas," he told the Seven Network.

"We're talking an area under fire right now of something like 370,000 hectares across NSW, a huge undertaking.

"There is a lot of work by firefighters necessary ahead of deteriorating weather conditions over the next couple of days."

Meanwhile, police are continuing to investigate a fire near Lithgow, in the Blue Mountains west of Sydney, which destroyed about 40,000 hectares on Wednesday.

It's believed to have been deliberately lit.

Since Tuesday, five people have been penalised for breaching the state's total fire bans on Tuesday and Wednesday, including three teenagers who are accused of deliberately lighting a blaze in Sydney's west.

NSW Premier Barry O'Farrell, who visited bushfire zones around Wagga on Wednesday, has backed plans to force arsonists to help put down animals injured in fires.

Mr O'Farrell and Prime Minister Julia Gillard have announced natural disaster assistance in 37 local government areas in NSW.