Firefighters have back burned through the night to get a handle on the massive blaze burning in the Hawkesbury region near Sydney's northwestern outskirts.
The Gospers Mountain fire, which is still burning out of control across more than 100,000 hectares, is at a "watch and act" alert level on Saturday morning after reaching an emergency level earlier on Friday.
A southerly change sweeping through the state eased the Gospers Mountain fire on Friday night, allowing firefighters to strengthen containment lines through back burning.
"This is important work which is being done ahead of worsening conditions next week," the NSW Rural Fire Service said in a statement on social media.
"People in the area will see an increase of fire activity as this is undertaken."
The biggest danger moves to the north of the state on Saturday - with severe ratings issued for New England, the Northern Slopes and northwestern regions.
Total fire bans are in effect in those areas, as well as the far north coast, on a day that will have temperatures moving into the mid-30s, very low humidity and gusty winds once again.
RFS deputy commissioner Rob Rogers says there is every prospect fires in these regions could return to emergency levels.
"Fires like that Gospers fire - that's a huge fire, 100,00 hectares it's burning out - that's not going to go out any time soon," he told Channel 7 on Saturday morning.
"When the warmer weather returns early next week we will see that start to head towards properties and we are really concerned about that fire."
National parks on the mid-north coast, north coast, and in the northern Blue Mountains remained closed to the public on Saturday morning due to fire danger, the NSW Office of Environment and Heritage said.
Bureau of Meteorology duty forecaster Bimal KC says a southerly change will bring some brief relief to other parts of the state on Saturday.
"The temperatures we are expecting are a little bit lower as the southerly change comes through," he told AAP on Saturday morning.
"On Sunday we are expecting similar conditions. Later on Tuesday the conditions will get worse as the heat starts building up.
"Tuesday and Wednesday will be fire weather days, with the weather conditions again deteriorating."
Five out of control fires were burning at a watch and act level on Saturday morning.
These fires were in Woodenbong, Willi Willi, Nambucca, Bora Ridge as well as the Gospers Mountain blaze.
The RFS said more than 150 brigades will open on Saturday morning to speak with residents across the state about their fire plans at the beginning of what is expected to be a long bushfire season.
The four people killed in bushfires over the past week are Barry Parsons, 58, at Julie Fletcher, 63, Vivian Chaplain, 69, and George Nole.
A man suspected of starting a blaze which sparked an emergency warning at Guyra Road in Ebor, east of Armidale, was arrested on Friday.
Australian Associated Press