A bushfire that threatened homes at Lithgow may have been deliberately lit.
Police Inspector Colin Cracknell said the fire was being considered as suspicious.
'There is some evidence this fire has been deliberately lit and a number of items of evidence have been collected,' he told Fairfax media on Wednesday.
'At this stage the investigation is ongoing.'
According to a NSW Rural Fire Service spokesman the fire, which has destroyed about 40 hectares of bushland, has been controlled.
He said earlier in the day some isolated properties in the region had been under threat, but had been saved by firefighters.
Variable winds and terrain have made the Lithgow fire difficult to contain.
Three helicopters have undertaken extensive water bombing and three dozers are on the ground enforcing containment lines.
Meanwhile the Princes Highway between Bendalong Road and Sussex Inlet Road is closed to allow firefighters to undertake a backburn near Wandandian.
The closure, from 9pm (AEDT), follows a reduced speed limit of 60km/h on the Princes Highway from Wandean Road to Bendalong Road, while Wandean Road and Twelve Mile Road also remain closed.
The Kings Highway also remains closed in both directions between Bungendore and Braidwood Road due to a bushfire.
Motorists are advised to use Braidwood Road to Tarago then Bungendore Road instead.
There is still no access from Nerriga to Nowra via Braidwood Road.