A golf-ball sized hole in Arkansas was the source of a unexplained flame that burned for 40 minutes in the early morning on September 17.

"As far as the spiritual Satan goes, we've ruled that out," County Judge Mickey Pendergrass said in a report by Arkansas online.

"He didn't come up and stick his pitchfork in the ground and blow that hole out."

However, Judge Pendergrass says the fire was likely started on purpose.

"What kind of fuel did they use to make it so clean and no soot and no damage? And what was used to strike the fire to start with? There are just too many questions for it not to have been done on purpose, whether it was for fun or for giggles," Judge Pendergrass said.

"Somebody will talk someday and have to brag about it, and then we'll find out who did it," he said.

The judge said he suspected methane, but none has been traced.

He said there were no utility and fuel lines in the area which could have leaked, and technicians from a nearby natural gas company detected no signs of natural gas, either.

The Arkansas Department of Environmental Quality is also stumped, after testing a total of nine tanks and concluding that none appeared likely to have contributed to the fire nor were leaking.

Ty Johnson, who works in the Geohazards section of the Geological Survey, believes soil samples from the hole, which are awaiting analysis, may hold answers.

Donald Tucker, chief of the Midway Fire Protection district, says he was unable to take photo or video of the flame as he was "trying to keep everyone away" from it at the time.

Mr Tucker said the flame was burning red-orange, and about 8 feet (about 2.5 m) high when he arrived.

County officials are satisfied that there is no risk of the fire spreading elsewhere in the neighbourhood.

The fire was on private property in front of a billboard advertising surgeon Dr Winn Morre, who says he has received a considerable amount of free publicity from the flaming hole.

Newshub.