Fumes spewing from the glowing pit are so hot that tree branches burst into flames when they are held over it.

Temperatures inside the opening are a whopping 792C, leading some locals to claim it is a portal to reach the Devil himself.

Construction workers discovered the mysterious lava-filled cave after spotting a small hole in on the surface of the hillside pouring out fumes last week.

Geologists are now flocking to study the unique sink hole on the outskirts of Urumqi, the capital of Xinjiang Uyghur Autonomous Region in north-western China.

The area was sealed off after the discovery of the phenomenon and scientists are now working to establish its origins.

Geologist Hu Tan who is leading the investigation into the 80 cm wide hole said: “The air blasting out of the hole is so hot, that if you hold a branch near to it it bursts into flames.

“Although it is unusual, we’re pretty certain that it has been caused by the spontaneous combustion of coal.”

Mining expert Cao Jianwen said the area was used as a coal mine in the 1970s and there have been previous documented examples of similar discoveries.

He said: “We have recorded a temperature of around 792 degrees Celsius, which is pretty hot and I can understand that locals are superstitious.”

Authorities are now moving in to seal off the opening over fears the toxic fumes could be harmful to those working in the area over long periods.

Mr Jianwen added: “I would not rule out that there could be similar sinkholes in this region in the future.”