“Several small fires were put out in the Lake Macquarie state conservation area at Crangan Bay, but smouldering material underground, extending along several hundred metres and up to five metres deep, had to be dug out,” the Newcastle Herald reported on Wednesday.

“The excavation to expose and cool smouldering chitter – waste from coal mining at the former Wallarah mine – was due to finish this week, with up to 20,000 cubic metres of material dug up.”

The slow-burning fire was reportedly first detected by rangers back in March after residents complained about the smell.

“Heat-detection radar was used to map it and investigators believe it started with bushfires in the Catherine Hill Bay area late last year,” the newspaper reported.

Mannering Park Progress Association subsequently questioned how an underground fire could have occurred there if the mine was closed and deemed rehabilitated three years ago.

While the Division of Resources and Energy was reportedly investigating the matter, a spokesman said “it was likely the fire got into the mine workings via tree roots”.