Surrounded in mystery and tales of demons, the Well of Barhout in Yemen's east -- known as the "Well of Hell" -- is a little-understood natural wonder.

Closer to the border with Oman than to the capital Sanaa 1,300 kilometres (800 miles) away, the giant hole in the desert of Al-Mahra province is 30 metres wide and thought to be anywhere between 100 and 250 metres deep.

Local folklore says it was created as a prison for the demons -- a reputation bolstered by the foul odours rising from its depths.

Yemeni officials say they don't know what lies below.

"It's very deep -- we've never reached the bottom of this well, as there's little oxygen and no ventilation," said Salah Babhair, director-general of Mahra's geological survey and mineral resources authority.

"We have gone to visit the area and entered the well, reaching more than 50-60 metres down into it. We noticed strange things inside. We also smelled something strange... It's a mysterious situation."

Sunlight doesn't extend far into the structure, and little can be seen from the edge except the birds that fly in and out of its depths.

Videographers seeking close-ups of the inside of the well have said they are almost impossible to capture -- local superstition has it that objects near the hole can be sucked towards it.

Babhair said that the well was "millions and millions" of years old.

"These places require more study, research and investigation," he said.

Over the centuries, stories have circulated of malign, supernatural figures known as jinns or genies living in the well.

Many local residents remain uneasy about visiting the vast hole, or even talking about it, for fear of ill fortune from a chasm which, legend has it, threatens life on Earth itself.

Yemenis have had enough bad luck as it is.

The country has been embroiled in a civil war since 2014 between the government and the Huthi rebels.

The United Nations says Yemen is suffering the world's worst humanitarian crisis, with tens of thousands killed, millions displaced and two-thirds of its 30-million population dependent on some form of aid.