The South and Mid Wales Cave Rescue Team said the man fell while caving in Ogof Ffynnon Ddu, a cave system near Penwyllt in the Brecon Beacons close to the village of Penwyllt in the Upper Swansea Valley on Saturday. Because of the injuries he suffered in the fall, he is said to be unable to climb out of the cave.

       The emergency service was notified by another caver and since then at least eight rescue teams from across the UK have joined the operation.

       The man has apparently injured his back, with more than 50 rescuers in attendence.

       Involved are the Gloucester Cave Rescue Group, Midlands Cave Rescue Organisation, Derbyshire Cave Rescue Organisation, Mendip Cave Rescue, South East Cave Rescue Organisation, the Cave Rescue Organisation, and Upper Wharfedale Fell Rescue Association.

       Located inside a nature reserve, Ogof Ffynnon Ddu - meaning Cave of the Black Spring - was discovered in 1946 and is 300m deep at its lowest point, with its underground caverns stretching to over 30 miles, making it Britain's deepest cave system as well as the third-longest.

       Only experienced cavers are granted permission to explore inside.

       A statement issued by the South and Mid Wales Cave Rescue Team (SMWRT) said: “On Saturday November 6th at 20:21 a male caver was undertaking a trip in the Ogof Ffynnon Ddu cave system and fell, resulting in some injuries that meant he could not exit under his own steam.

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       “A fellow caver notified the police, and the South Wales Caving Club initiated a response.

       "The incident is ongoing and involves rescuers from teams across the UK.

       “Their response to the incident continued during the night and we are currently moving the casualty towards the top entrance of the cave, which is located up on the mountain behind Penwyllt.”

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       Pictures from the scene showed experts with rescue equipment at the scene.

       South Wales Caving Club's onine guide says of Ogof Ffynnon Ddu: “The through trip from the top to the bottom entrance remains a classic in the UK, and its approximately 61km of passages provide everything from huge chambers, beautiful formations, to yawning chasms and thundering river passages.

       "The routes through the cave are too numerous to mention.

       It warns: "Be aware that the mainstream and some other parts of the cave are prone to flooding, and in any event a journey down the mainstream is long and cold and wet, so go prepared."

       Posting on Facebook, Upper Wharfedale Fell Rescue Association (UWFRA) said: "UWFRA have deployed a small team of cavers to assist in an on going rescue in Ogof Ffynnon Ddu in South Wales. Multiple teams from the South have been assisting and, yesterday afternoon, the British Cave Rescue Council - BCRC requested further assistance from the Northern teams.

       "Our team travelled down overnight and got a few hours sleep before joining the rescue this morning.

       "We wish all the Teams involved a safe trip and a successful outcome."