At least three Coalfields homes were damaged and two firefighters were taken to hospital after suffering the effects of smoke inhalation as catastrophic bushfire conditions lived up to their name, with blazes raging at emergency warning level at North Rothbury and Greta yesterday afternoon.

Greta resident John Brittin fled his home of 20 years at the top of Leconfield Road thinking the fire would claim it.

He told the Newcastle Herald the blaze roared through the paddock across the road, burning an area of "about 200 metres in probably 30 seconds".

"I stayed until [the police] told me to go," the 68-year-old said. "I left thinking the house was gone."

The fire burned just about everything but his home - literally right up to the door. The shed suffered partial damage.

"I feel like I've won the lotto," Mr Brittin said.

As spot fires continued to flare up around his home and with water bombers circling in the air, Mr Brittin thanked the mainly Victorian firies who had saved his house.

"These firies - 95 per cent of them are volunteers. Just the way they upend themselves. Not many countries in the world have got a fire service like this," he said.

Rural Fire Service crews battled the dire weather conditions across much of the eastern part of NSW throughout Tuesday, after a seven-day State of Emergency was declared ahead of hot, dry and windy conditions.

"It's literally as bad as it gets," RFS Lower Hunter operations officer Terry Burns told the Newcastle Herald last night.

"Crews have been battling fires in strong winds and hot temperatures.

"They have done an excellent job, the crews out on the ground, to do what they've done."

As of yesterday evening, there were 85 fires burning across NSW - 46 were not contained, 14 were at emergency warning level and seven were rated watch and act.

The blaze near Wine Country Drive at North Rothbury, about 8km from Cessnock, was upgraded to an emergency warning rating at about 2.30pm but was downgraded to advice level by the evening.

"Property is under threat," the RFS told residents on social media as the fire flared.

"If you are in the area of North Rothbury, it is too late to leave. Seek shelter as the fire approaches."

Three properties were damaged as the fire impacted the town, RFS confirmed, though Mr Burns said the extent of the damage remained under investigation last night.

A fast-moving grass fire then broke out at Harper Street, Greta, at about 4pm - about 6km from North Rothbury.

Residents were told to "seek shelter as the fire approaches". It was downgraded to watch and act by the early evening.

Mr Burns said 30 fire trucks and an aircraft remained at the Greta fire working to contain it just after 6pm, while 12 crews were mopping up at North Rothbury.

A NSW Ambulance spokeswoman said two firefighters - a man and a woman, each aged in their 40s - were treated for smoke inhalation after they collapsed at North Rothbury.

She said the man was also suffering from dehydration and heat exhaustion and was taken to Maitland Hospital in a stable condition.

RFS commissioner Shane Fitzsimmons said wind gusts of up to 80km/h had been recorded in the Hunter through the afternoon.

"We are seeing very strong winds coming down through the Hunter Region ... which is influencing a deal of this fire behaviour," he said.

Homes on the parallel Harper and York streets were some of the first to come under threat in Greta.

Harper Street resident Brock Taylor was at work when the fire took hold.

"I rang the wife about lunchtime, she said 'everything's fine, it's over at North Rothbury and Whittingham'," he recalled.

"Then I heard on the radio Harper and York streets had been evacuated. I rang the wife as quick as I could and she said she'd just been evacuated.

She said the fire was two doors up and hen she drove off the fire was coming straight on."

Mr Harper said his wife "packed up a few things; photos, birth certificates, passports, those sorts of things" and got out.

He raced home, finding the fire only metres away from his front fence on the other side of Harper Street, where this is vacant property and relatively thick scrub.

"There was a fire in the garden but thank Christ nothing ever happened [to the house]," the 42-year-old said.

"We've been here 13, 14 years, this hasn't been up in that time. We knew it was going to happen one day. It's disastrous.

"It's probably a good thing now, we'll be safe for the summer. Safe for another couple of years."

Two doors down and closer to the fire, Peter Searle's wife Joanne was home with six grandkids under the age of seven when the fire hit.

Mr Searle said "she bolted with those" while he raced home from work, seeing smoke in the "line" of his property as he "came up the highway".

"I thought that doesn't look good," he said. "I grabbed a hose and started hosing all the stuff I should have cleaned up on the weekend.

"We're bloody lucky in this street.

"Luckily the Victorian guys who have been up at Singleton Army camp waiting, they got a call and came here and got on top of it. There was about seven or eight tankers that came up.

"If they were out at a fire - god knows."

Mr Searle, 65, said he had lived at his home, which fronts York Street and backs onto "very dense" scrub, for about 29 years and had "never seen a fire" until Tuesday.

"It was very close," he said. "The wife's very shaken up."

Catastrophic bushfire weather swept through the Hunter as predicted. Temperatures reached 36 degrees at the Maitland and Williamtown weather stations, with Nobbys recording a top of 33.

Conditions are expected to slightly ease on Wednesday, before hot, dry and windy weather returns to the eastern part of the state at the end of this week.

All Hunter RFS stations were on stand-by on Tuesday and firefighters were waiting through the morning to see whether the catastrophic conditions would deliver any challenges.

"Everyone has probably got a knot in their tummy because if something happens, we don't know which way it's going to go," Medowie RFS senior deputy captain Peter Smith said before the Hunter fires took hold.