The RFS has declared the highest fire danger rating for three regions, including Illawarra/Shoalhaven and Southern Ranges, with temperatures expected to climb above 40 degrees.

Southern Ranges takes in Goulburn Mulwaree, Yass Valley and Upper Lachlan Shires and Queanbeyan Palerang Regional Council.

It comes as Premier Gladys Berejiklian declares a State of Emergency for Saturday.

The Rural Fire Service is expecting dangerous fire conditions in the sweltering heat sweeping the state.

The Bureau of Meteorology says a trough will move through NSW. Hot and gusty westerly winds ahead of the trough will drive the fire conditions.

On Friday, Goulburn's air quality deteriorated to the worst in the state. The air quality index reached 2266 at its peak between 2pm and 3pm, Department of Planning, Industry and Environment data showed. The nearest to this leval at the same time was Orange on 1102. Anything above 200 is considered hazardous.

By 7pm to 8pm, the index had fallen to 1113, still the highest in the state behind Bathurst on 1071.

Residents holed up indoors while some wore face masks around town. The heavy haze forced the cancellation of Goulburn and District Race Club's meeting.

West Goulburn resident Lindsay Allen took his own readings on his air quality monitor at 6.30am Friday. It measured 999.9 for both PM10 and PM2.5 pollution particles. PM2.5 particles can be breathed deep into the lungs and cause respiratory problems.

Mr Allen said the readings, which unlike those at the Department's monitoring station in Legget Park were not averaged but actual, were the worst he had measured since the fires started.

The smoke was mainly blowing over from the Currowen fire in the Shoalhaven, which has so far burnt out 128,461 hectares. The Green Wattle Creek fire in the Wollondilly Shire has also destroyed 176,460ha.

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The latter has intermittently cut Hume Highway access and stopped trains running between Campbelltown and Moss Vale on Friday. However, he train service was running between Moss Vale and Goulburn.

Meantime, state agencies government have issued the following advice. People are urged to share this with family and friends.

Due to the proximity of current bushfires to main roads and highways, it is anticipated that many of these roads will close tomorrow.

It is expected that this will occur on the Princess Highway near Sussex Inlet as well as other sections of the Princess Highway near the Currowan fire; the Hume Highway near Narellan, the Great Western Highway near the Blue Mountains and possibly the F1 near the Central Coast as well as other northern sections of the F1 where fire activity is already occurring.

If you require emergency assistance call 000.

Catastrophic is the highest level of bush fire danger. Homes are not designed to withstand a fire under these conditions.

If a fire starts and takes hold during Catastrophic fire danger conditions, lives and homes will be at risk.

Large areas of the state are also forecast to experience Severe and Extreme fire danger. This includes the Hunter and Central Ranges areas.

Currently there are more than 100 fires burning across NSW, of which more than half are yet to be contained. These fires will not be contained in time and will threaten lives and properties.

A state-wide total fire ban remains in place until at least midnight Saturday, December 21.

Motorists should delay all non-essential travel.

Many roads continue to be impacted by fire and major roads may be closed suddenly and without warning:

If you need to travel:

If you're already travelling when a bush fire starts, follow the directions of emergency services personnel.

Due to fire activity, both main and local roads may close without warning. For the latest information on road closures, check www.livetraffic.com or download the Live Traffic NSW app or call 132 701.

For the latest information on public transport, check www.transportnsw.info or download a transport app or call 131 500.

Strong winds may impact NSW from Thursday across the weekend. Take the time now to prepare your home or property and be aware of weather conditions:

People with any respiratory issues or who are particularly vulnerable can be the first to feel the effects of smoke which may aggravate their existing condition. Even healthy adults and children can be impacted by the effects of heavy smoke which can result in lung irritation.

These conditions can have a serious impact on your health and it is important to remember that our bodies have to work extra hard to cope or cool down. Ensure you stay hydrated and pay particular attention to any symptoms (dizziness, headaches, racing pulse or nausea) of heat related illness.

If you are preparing to leave, make sure you pack your medications, including those in the fridge.

Smoke can cause health problems, particularly for people with pre-existing lung and heart conditions like asthma, emphysema, angina or heart failure.

Avoid outdoor physical activity if it's smoky, particularly if you have a pre-existing condition like asthma.

People with asthma should follow their asthma management plans.

If you have asthma, make sure you keep your reliever medication close to hand.

If your reliever medication has run out or is passed its use-by date, you can buy a new one from the pharmacy without a prescription.

You can reduce exposure to smoke by staying indoors with the doors and windows shut. Air conditioning can help to filter out smoke that gets into your house.

The following link contains a fact sheet with information about what to do if fire retardants have been used on your property and may have affected your private drinking water supply:

https://www.health.nsw.gov.au/environment/factsheets/Pages/fire-retardants.aspx

Be aware of potential hazards such as embers, falling debris, damage to surroundings and reduced visibility which can cause injury.

Paramedics are urging people in fire affected areas to wear any form of eyewear and loose clothing to cover your skin to assist in reducing any incidental injury.

NSW Ambulance recommends if anyone sustains any form of burn they should cool the affected area immediately with water - ideally running water - for a minimum of 20 minutes (for eyes ensure you flush the eye) and seek medical attention.

It is important that people really take care of themselves. If you have a pre-existing medical condition, make sure you have all your medications with you and readily available at all times.

People with any respiratory issues, or who are particularly vulnerable, can be the first to feel the effects of smoke which may aggravate their existing condition. Even healthy adults and children can be impacted by the effects of heavy smoke which can result in lung irritation.

These conditions can have a serious impact on your health and it is important to remember that our bodies have to work extra hard to cope or cool down. Ensure you stay hydrated and pay particular attention to any symptoms (dizziness, headaches, racing pulse or nausea) of heat related illness.

NSW Ambulance is always here to help - never be afraid to call Triple Zero.

There are evacuation centres open in some areas, however your best choice is to relocate to the homes of family or friends in an area not under threat of bushfire.

Relocation from an area under threat of fire may take longer than a few hours; ensure you take essential living items with you, including medication and support items.

Don't forget your pets! Make arrangements for their relocation now. Domestic pets may be taken to evacuation centres; there are other facilities available for larger animals.

The most up to date information regarding Evacuation Centres (for people and animals) can be found at: https://www.emergency.nsw.gov.au/Pages/for-the-community/disaster-assistance/disaster-assistance.aspx

Include your animals in your bush fire plan.

If you can, take your animals with you. Assistance from Agriculture and Animal Services Functional Area (AASFA) is available if you attend an evacuation centre.

For those impacted and seeking assistance for emergency fodder, emergency water (for immediate animal welfare cases only) or animal assessment (resulting from the fires) please contact the AASFA Hotline on 1800 814 647.

Keep at least eight metres away from fallen power lines or objects that may be energised, such as fences.

Report fallen power lines to either Ausgrid (131 388), Endeavour Energy (131 003), Essential Energy (132 080) or Evoenergy (131 093) as shown on your power bill.

A full list of the closures is available at https://www.nationalparks.nsw.gov.au/alerts

A full list of the closures is available at https://www.forestrycorporation.com.au/__data/assets/pdf_file/0008/1193381/closures-20-december-2019.pdf

Whilst the land is the most impacted, we are encouraging general public to also stay off the water.

Given the catastrophic conditions across the state, NSW Maritime encourage boaters to stay off the water in the coming days until conditions improve. The fires are extremely unpredictable. So please take all the necessary precautions and put safety first.

Other Information

A total fire ban has been issued for the whole of the state of NSW until midnight Saturday, December 21.

If you need emergency assistance call Triple Zero (000).

Anyone who sees suspicious or illegal behaviour is urged to contact police via Crime Stoppers on 1800 333 000 or https://nsw.crimestoppers.com.au. Information is treated in strict confidence. The public is reminded not to report crime via NSW Police social media pages.