Tuesday's fire danger is expected to be worse than originally forecast after the NSW Rural Fire Service (RFS) extended its "catastrophic" warning to coastal cities south of Sydney.

On Monday afternoon, another 400,000 people across the Illawarra and Shoalhaven areas were warned to prepare for the worst ahead of what NSW Police Minister David Elliot said could be "the most dangerous bushfire week this nation has ever seen".

Key points: More than 350 schools and TAFE campuses will be closed tomorrow

More than 350 schools and TAFE campuses will be closed tomorrow Greater Sydney, Greater Hunter, the Illawarra and Shoalhaven regions have catastrophic fire danger warnings in place

Greater Sydney, Greater Hunter, the Illawarra and Shoalhaven regions have catastrophic fire danger warnings in place More than half of the 60 fires burning in NSW remain uncontained

A million hectares have now been razed across New South Wales since the start of this year's unprecedented bushfire season.

Three people were killed and at least 150 homes destroyed on the state's mid-north coast and northwest where bushfires ravaged regional towns at the weekend.

NSW Premier Gladys Berejiklian declared a state of emergency, warning residents "for heaven's sake, stay away from bushland tomorrow".

Over 350 schools and TAFE campuses will be closed tomorrow — this number could rise throughout the day.

It's the first state of emergency in NSW since October 2013, when major bushfires swept the state in similar weather conditions, combining gusty winds and hot, dry land.

The RFS said "catastrophic" conditions were expected in Greater Sydney and the Greater Hunter on Tuesday, before extending the warning to the Illawarra and Shoalhaven.

It is the first time the Sydney region, including the Blue Mountains and Central Coast, has faced a catastrophic warning in the 10-year history of fire danger ratings.

Hot, windy conditions are forecast to stoke more devastation, with temperatures set to soar into the mid-30s.

Police Minister David Elliot said the forecast conditions could potentially lead to "the most dangerous bushfire week this nation has ever seen".

Anthony Clark from the RFS warned the coming conditions would be "as bad as it gets".

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 44 seconds 44 s NSW RFS chief outlines catastrophic fire risk

More than half of the 60 fires burning in NSW were uncontained on Monday, with 10 of them at watch and act.

A state of emergency grants emergency powers to the RFS, including the coordination of evacuations, extended access to government resources, traffic redirections, the power to shore up or demolish buildings, and power to shut down gas, electricity, oil and water services.

"There's a lot of hard work ahead of us, but the simple message is we're not going to get on top of those fires before these really bad conditions hit on Tuesday," Mr Clark said.

People in bushfire-risk areas have been told to start thinking now about a survival plan and head to larger towns and built-up areas.

Commissioner Fitzsimmons warned, "we cannot guarantee a fire truck at every home" and encouraged early evacuation for those at risk.

"If you're not doing that tonight, you certainly need to be doing it early tomorrow morning," he said.

"We know the fires on the northern coast are not going to be contained ahead of tomorrow's weather, which means those fires are going to spread, they're going to spread quickly and spread aggressively."

A total fire ban is in place statewide for Monday and Tuesday and some schools have been closed.

Commissioner Fitzsimmons said more than 1,400 personnel from interstate had joined the firefighting effort in NSW and 400 more were set to arrive on Monday ahead of Tuesday's dangerous conditions.

He said up to 20 firefighters had already accessed medical attention in hospitals as blazes intensified.

Scenes at Johns River on the Mid North Coast on Sunday. ( ABC News: Mridula Amin )

Early signs of carnage

At the end of August, the RFS brought forward by a month the start of the bushfire danger period for more than 70 local government areas, as a precaution against the looming warm, dry conditions.

Within a week, homes were lost as fires tore into communities across the state with northern NSW near Tenterfield among the worst-hit.

Commissioner Fitzsimmons said it was an indication of the severity of the coming bushfire season.

"It is a sobering reminder of what is ahead, with the outlook indicating the next three or four months is dominated by above-average temperatures, below-average rainfall and unfortunately there is no meaningful signal anywhere for drought-breaking, relieving rain," he said.

Last month, two people died as fires again tore through northern NSW, with 45 homes destroyed in the onslaught, before the latest statewide crisis hit last week with an unprecedented 17 fires at emergency level on Friday.

Community faces anxious wait to get home

One of the communities worst hit by last week's outbreak of fires was the small town of Wytaliba, near Glenn Innes in the state's north.

Richard and Katie Taylor, with their children Madeline, Grace and Gus (L to R), were anxious to get home. ( ABC News: Paige Cockburn )

On Sunday, many residents spent the day waiting at a roadblock in hope of reconnecting with loved ones who had been trapped inside the devastated community after it became too late to leave.

For Richard and Katie Taylor, who own a now-charred cattle property just outside of Wytaliba, the lock-out was worrying as it meant their cattle had to wait even longer for food and water.

"This is just another little challenge we have to deal with," Mr Taylor said.

Plumes of smoke as seen at Wytaliba on Sunday. ( ABC News: Paige Cockburn )

Fire continues to burn in the remote area, making it still too dangerous to reopen the roads.

Two people from the area, George Nole and Vivien Chapman, died when the massive inferno ripped through.

Almost all properties are expected to have been destroyed.

A local police officer at the roadblock told the ABC that what he had seen inside the community was too confronting to speak about.

Long-time Wytaliba resident Danielle Monks waited at the closed road for eight hours on Sunday, desperate to deliver food and water to those who were stuck inside, including her husband and daughter.

"They haven't eaten properly since Friday … the snacks have all run out," she said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 11 seconds 1 m 11 s Residents at Johns River, seen here fighting Friday's blaze, are in the middle of another emergency.

The Taylors' house was fortunately spared, which they owe to their neighbour who cut a fire break around their home when he realised they would not make it back in time to begin property protection.

"It was really good country spirit … the way things should be," Mr Taylor said.

A fire break was even dug around a cow who had just given birth on the Taylor property, which ensured the animals' survival as the blaze swept around them.

The cause of the Wytaliba fire is under investigation.