A large fire burning in Lithgow on the western side of the NSW Blue Mountains is threatening 20 properties, sparking an emergency warning.
The NSW Rural Fire Service (RFS) says the blaze, which has burnt through 30,000 hectares, is threatening properties in the small township of Bell and residents are advised to take shelter.
"Fire activity has intensified in the Bell area," a spokesman said.
"There's about 20 properties in the community of Bell which are under threat at the moment.
"We have upgraded it to an emergency warning and we're sending out emergency alert phone messages in that area right now."
The defence department is investigating whether there is a link between the fire and an explosives training exercise that took place at the Marrangaroo training area on the same day.
Premier Barry O'Farrell said he had not been briefed on the investigation.
An RFS spokesman told AAP there were no fire bans while Defence was holding the training on October 16 and that it occurred a day before extreme conditions were expected.
Mr O'Farrell said defence had been helping in dealing with the Lithgow fire because it broke out on defence land as explosives were being detonated.
"I do know that yesterday when we were in Lithgow being briefed by the incident controller, he made the point that the defence agencies had been helpful in dealing with the State Mine fire because it did start on defence land," Mr O'Farrell said.
"I know for a fact he told me that at one stage they stopped any aircraft flying over that area because of those exploding ordnances."He said "there was no suggestion from the incident controller" that defence explosives testing had sparked the blaze.