A total fire ban is in place for the local government area with the mercury expected to soar and December temperature records will be smashed.

A maximum of 38 degrees is predicted for Oberon and, if reached, it will surpass the town's hottest ever December day of 35 degrees recorded on December 30, 1965.

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NSW RFS Chifley/Lithgow district assistant Michael Dunn said firefighters would have their "eyes everywhere" on Tuesday due to a severe fire danger rating.

"With that kind of fire danger it has the potential to increase fire activity," he said.

The Gospers Mountain bushfire, which has been burning in the Lithgow local government area for the past six weeks, has now grown to more than 309,000 hectares and Mr Dunn said it would likely get bigger on Tuesday.

The current perimeter of this fire is now 950 kilometres long, which is the equivalent of driving the distance between Sydney and Brisbane.

Mr Dunn said people living near bushland areas should make the decision prior to a fire on whether they will leave their property or stay and defend.

If people choose to stay, he said the land around properties should be cleared of any flammables, leaves should be cleaned from gutters and the home owner should have firefighting equipment on hand.

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"You need to make sure you've got hoses long enough to reach right around your property," he said.

Mr Dunn said the community could play a part in preventing new fires during such hot, dry weather.

"We're encouraging people not to do any hot works on the day that could create a spark and start a fire, that includes grinders, welders and slashers," he said.

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"We've had three fires ignite this way during the past two weeks."

Widespread smoke is expected to continue across the region due to ongoing bushfires, with the air quality alert still at hazardous levels in the Central Tablelands on Monday afternoon.

Stay up-to-date with fires in your area at Fires Near Me or call the Bushfire Information Line on 1800 679 737.

Call triple-0 if you see an unattended fire.