The auction of a South Sydney Rabbitohs cap owned by Australian actor Russell Crowe has generated $400,000 in donations.

In a video message, NSW RFS Commissioner Shane Fitzsimmons said firefighters were grateful and humbled by the outcome.

"What he claimed started out as a random silly idea is certainly far from it when it comes to the men and women of the Rural Fire Service up north," Commissioner Fitzsimmons said.

We tip our hat to you, @russellcrowe 🧢 What an amazing and generous show of support for our incredible volunteers!#nswrfs #nswfires pic.twitter.com/FYSS1B9FKn — NSW RFS (@NSWRFS) November 29, 2019

"And indeed it is reflective of the extraordinary generosity that we're seeing right across New South Wales and much further afield."

The fire chief said an official RFS cap is on its way to Crowe to replace the one that was auctioned.

"It might not be as well worn. But we're going to send this your way."

The 'slightly worn' Rabbitohs cap fetched $US68,000 in a Twitter auction that ended on Friday morning (7.21am AEDT).

Crowe had promised to double or triple the price of the hat in a donation to the NSW Rural Fire Service and has since delivered a cheque for $105,000 to the rural firefighters.

So... delivered 19 cheques to RFS Captain John Lardner, a total of $105k because I cant count apparently,

haha all good@NSWRFS pic.twitter.com/QlCEXMBlm6 — Russell Crowe (@russellcrowe) November 29, 2019

But the act encouraged others to make six-figure donations to the NSW RFS.

Mr Cannon-Brookes said he would also give $5,000 to each of the 20 RFS brigades.

Atlassian co-founder Scott Farquhar and US software company Qualtrics CEO Ryan Smith said they would each make a $100,000 donation.

Mr Cannon-Brookes praised Crowe for inspiring the acts of generosity.

"You’ve started something amazing here," he tweeted.

"Your hat has now generated $400k in donations in 24h to help tired, exhausted fireys!"

Hey @russellcrowe @NSWRFS - you've started something amazing here.



Unasked, both @scottfarkas and @RyanQualtrics are matching the $100k as well. Total legends both of them! 👏🏻 Thank you both!❤️



Your 🧢 has now generated $400k in donations in 24h to help tired, exhausted fireys! https://t.co/Wp7W2lQbD7 — Mike Cannon-Brookes 👨🏼‍💻🧢 (@mcannonbrookes) November 29, 2019

Crowe said he was inspired to auction the hat after firefighters saved his property near Coffs Harbour.

"I want to thank the volunteers all over the state and all over the country that work tirelessly to keep our communities safe," he said in a message posted on Twitter.

He said seeing the scarred bushland around the property emotionally affected him.

"Fires still burning, logs smoking everywhere you look," he posted in a tweet on November 25 as he surveyed the damage.

Firefighters and aicraft are working hard to protect properties west of Braidwood. The North Black Range fire is spreading quickly, with numerous spot fires starting ahead of the main fire front. The fire is at Emergency Warning level. #nswrfs #nswfires pic.twitter.com/d4CbolPzqp — NSW RFS (@NSWRFS) November 29, 2019

NSW RFS are continuing backburning efforts as it monitors 160 fires across the state.

Total fire bans are in place for the Greater Hunter, Central Ranges on Saturday.

The Bureau of Meteorology has forecast cooler temperatures for the state's south on Saturday.

But warm weather and wind are expected to continue in northern New South Wales over the weekend.

On Friday evening, air quality remained compromised with "hazardous" levels on North-west slopes and Northern tablelands.

"Very poor" air quality levels have been listed for the Central tablelands, Lower Hunter, Illawarra, Sydney north-west, Sydney south-west and Sydney east.