Residents in Sydney are urged to be on high alert as a sweltering 43C is forecast in areas where out of control bushfires are already bearing down on homes.
Firefighters had another tough day on Saturday battling blazes including the massive Gospers Mountain mega fire near Sydney's northwestern outskirts, which has merged with neighbouring fires.
Conditions eased on Sunday, allowing firefighters a chance to do critical back-burning ahead of Tuesday, when the mercury is tipped to soar into the 40s in parts of the state.
NSW Rural Fire Service Commissioner Shane Fitzsimmons told Seven News on Sunday: 'We've got much more benign conditions, particularly a dominant easterly influence which will stretch pretty much right across most of our fire grounds.
Residents in areas of Sydney were bushfires are already burning are urged to prepare ahead of Tuesday's forecast, which could reach 42C in some parts. Pictured: Beachgoers at Milk Beach on Saturday
'Which means hundreds - as a matter of fact more than 1600 - firefighters are around again today doing really important and critical back burning and containment-line consolidation.'
Mr Fitzsimmons said the measures were to 'try and gain the upper hand' before conditions deteriorate into Tuesday.
The Gospers Mountain fire, which is more than 304,000 hectares in size, is burning in the Wollemi National Park area.
Residents in Glen Alice, Wolgon Valley, Ovens, Olinda Valley, Lower Portland, Central Colo, Colo, Upper Colo, Colo Heights, Mountain Lagoon, Upper Macdonald, Perrys Crossing, Fernances and Mogo Creek, Blaxlands Ridge East and East Kurrajong areas are advised to 'continue to monitor conditions' and 'be ready to take action in case conditions change'.
The Bureau of Meteorology tweeted a warning on Sunday that much of inland NSW would 'swelter' through a heatwave early this week.
'With hot 40-plus-degree days and very warm 20-plus-degree nights,' the bureau tweeted.
'Stay hydrated, keep cool, look out for the vulnerable and beat the heat.'
According to the Bureau, Penrith and Richmond could hit 42C on Tuesday, while Liverpool and Campbelltown are expected to reach 40C.
At 9pm on Sunday, there were 91 bush and grass fires burning across NSW and 48 were uncontained. Pictured: Firefighters try to contain an out of control fire near properties west of Newcastle last week.
'Hot and mostly sunny. Areas of smoke haze,' the forecast reads.
The Green Wattle Creek fire burns west of Campbelltown and the Gospers Mountain blaze is raging north-west of Richmond.
At 9pm on Sunday, there were 91 bush and grass fires burning across NSW and 48 were uncontained.
There were five blazes which remained at Watch and Act, NSW RFS said.
'Crews have worked hard today locking in containment lines, being supported by aircraft and heavy plant as well as making safe roadways to try and re-open them,' NSW RFS wrote on Facebook.
'A number of community meetings were also held today providing updates to residents on the current fire situation and what they should do to prepare, ahead of increased fire dangers on Tuesday.'
The Bureau of Meteorology tweeted a warning on Sunday that much of inland NSW would 'swelter' through a heatwave early this week
NSW RFS spokesman Greg Allan told The Daily Telegraph fires are named by the location in which they started.
'Not all times will a fire be named after a suburb, town or road so it's very important people stay up to date with the web, radio or other media,' Mr Allan said.
Mr Allan also spoke of the warm weather looming in on Tuesday.
'The forecast for that southerly change means any fires currently burning would change direction, which is when conditions become very dangerous because you have that large fire front,' he said.
Hawkesbury City Council mayor Barry Calvert also stressed his concern about the massive Gospers Mountain blaze amid Tuesday's forecast.
'In Richmond they're expecting temperatures of about 43C and the wind will be coming from the west or northwest toward Blaxlands Ridge and East Kurrajong, where there are a lot of properties to defend,' he told the publication.
According to the Bureau, Penrith and Richmond could hit 42C on Tuesday, while Liverpool and Campbelltown are expected to reach 40C. 'Hot and mostly sunny. Areas of smoke haze,' the forecast reads. Pictured: NSW RFS crews north of Sydney on Friday
Air quality in Coffs Harbour, Bathurst, Tamworth and Gunnedah also reached hazardous levels on Sunday evening.
'Very high' fire danger is in place for Monday for the greater Hunter, Illawarra/Shoalhaven, Monaro alpine, southern ranges, central ranges, northern slopes and north-western fire regions, as well as the ACT.
Prime Minister Scott Morrison visited the RFS Control Centre in the Hawkesbury on Sunday.
Mr Morrison attended for a briefing and update from Superintendent Karen Hodges and her team 'who are doing a great job,' Mr Fitzsimmons posted on Twitter on Sunday afternoon.
'The PM also delivered a message of thanks to crews in the field, via the radio network.'
NSW Rural Fire Service crews assemble at a staging area as the Wrights Creek fire approaches Kulnura on the NSW Central Coast on Friday