A large bushfire burning in the NSW Hunter region has been downgraded to advice amid easing conditions, as former prime minister Tony Abbott joined fire crews battling the blaze.

Key points: The blaze had threatened homes for most of the day

The blaze had threatened homes for most of the day Strong winds of up to 90kph fanned the flames

Strong winds of up to 90kph fanned the flames Boeing 737s were used was waterbombers in a world first

At one point, strong winds and turbulence grounded large waterbombing aircraft fighting the fire, which has burnt through about 1,700 hectares at Salt Ash, north of Newcastle.

The bushfire was declared an emergency early on Friday morning as strong winds continued, however it was downgraded to watch and act as conditions eased about 4:00pm.

It was further downgraded to advice around 8:00pm.

Mr Abbott and his Davidson Brigade were among 268 firefighters working in the area to protect homes.

NSW Rural Fire Service (RFS) said firefighters would remain on the fire ground overnight to strengthen containment lines and backburning would be done if weather conditions allowed.

Commissioner Rob Rogers said while the fire had been downgraded, the threat was not over.

"While ever these strong winds persist, then there's always going to be a risk of the fire jumping containment lines and becoming a problem again," he said.

Fire crews battle fire near houses along Lemon Tree Passage Road, in Salt Ash. ( AAP: Darren Pateman )

Mr Rogers said firefighters had been working in "extremely difficult conditions" with winds gusting up to 90 kilometres per hour and causing the large air tankers to be grounded.

"When something that big that can't handle that sort of turbulence and those conditions, then you know the conditions have been bad."

Throughout the day, ember attacks caused new spot fires ahead of the fire front, Mr Rogers said.

"You could see that fire, it was really intense and you could see the number of embers that were being thrown out well ahead of that fire and starting new fires," he said.

"That area and those residents have been under quite a sustained attack from 24 hours now so I'm sure it's been an awful experience for them."

It is the third major bushfire in the area this year.

Former prime minister Tony Abbott (left) takes a breather on Lemon Tree Passage. ( AAP: Dan Himbrechts )

Mr Rogers said firefighters were expecting conditions on Saturday to be windy again, but "nowhere near the strength" of Friday's winds.

Conditions were expected to ease further on Sunday.

Adding to the challenges for crews and residents are mobile phone reception issues affecting the Optus network in the Port Stephens area, which has caused problems with calls, text and internet.

Mr Rogers said reopening the road was a priority for firefighters once it was safe, due to the large number of residents wishing to get home.

Sorry, this video has expired A firefighting aircraft dumps water on the flames of the Salt Ash bushfire

Desperate fight to save homes

The blaze came within 100 metres of Tania Craig's property on Lemon Tree Passage.

"I'll leave if we're told to go, definitely, I wouldn't stay," she said.

"You do get emotional, I got a bit teary but then I was like oh quick we've got to do this, we've got to do that. So you kind of forget about that and just act."

Firefighters have been told winds are expected to be stronger Friday than originally forecast. ( AAP: Darren Pateman )

An evacuation centre at Irrawang High School, which was set up on Thursday night, has now been closed.

Salt Ash Public School students were relocated to Fern Bay Public School, about 16 kilometres away.