Local NSW police have started to alert the residents of Kybean Valley of potential exposure to a raging bushfire that started near the Mount Forest Road, Carlaminda area.

"That is now impacting on homes. We have trucks there and firefighters obviously, we've also got some water bombing aircraft," Ben Shepherd, NSW Rural Fire Service spokesman, told reporters in Sydney on Tuesday.

So far, no homes have been destroyed, he said.

As of press time, police are knocking on the doors of each of the houses in the valley to advise the impending ravaging fire, which has already crossed over the Numeralla River.

"Seek shelter if the fire impacts. Leave only if it is safe to do so. Protect yourself from the radiant heat," the NSW Rural Fire Service advised residents.

At the same time, the fire service told residents in the Dangelong, Numeralla and Countegany areas to remain on alert as the fire could cross over to their localities.

More than 100 fires are currently burning across the state in different localities. About 20 are still uncontained.

Police said the 500ha scrub and grass fire at Carlaminda in the Yarrabin area pose immediate threat to property.

NSW residents have been alerted to brace for one of the "catastrophic" fire threats in the state's history on Tuesday as temperatures are forecast to surge above 40 degrees in most parts of the state, including Sydney.

A total state-wide fire ban has been issued for Tuesday. A catastrophic rating had been put in place for the Illawarra, Shoalhaven and Southern Ranges.

Many other areas as well are likewise expecting extreme danger levels.