The Greta fire has been downgraded to Advice level.
The large air tanker conducted a second run over the fire, which helped ground crews gain the upper hand.
Leconfield Road remains closed while 20 RFS crews and six Fire and Rescue NSW teams remain on scene.
A large air tanker has flown over the Greta blaze and delivered a line of fire retardant to slow the fire's progression.
"It will also give us the opportunity to protect properties," Lower Hunter Rural Fire Service operational officer Guy Baddock said.
The fire is being controlled and Mr Baddock said crews were in a better situation than when the fire was upgraded just after 12pm on Wednesday.
INITIAL REPORT 12.20PM
The fire at Harper Street, Greta has been upgraded from Advice level to Watch and Act after it breached containment.
About 40 firefighters are currently on the ground but Lower Hunter Rural Fire Service operational officer Guy Baddock said about 30 more and an aircraft were on their way to assist.
Leconfield Road will be blocked while firefighters start suppression activity. A house has been evacuated.
Mr Baddock said a combination of dry vegetation, wind and damage from yesterday had caused the flare up.
He urged residents to follow directions from firefighters, follow their bushfire survival plans and stay up to date on the Fires Near Me app.
Mr Baddock said the causes of the Greta and North Rothbury fires were under investigation and both were being treated as suspicious, but stopped short of saying they were deliberate.
"Saying anything beyond suspicious would be speculation," he said.