Rescuers have described how a man became trapped inside a cave system in the Brecon Beacons for two days, triggering the longest rescue operation in the area's history.

The South and Mid Wales Cave Rescue Team said the man fell while caving in Ogof Ffynnon Ddu near Penwyllt on Saturday.

He is unable to climb out because of the injuries he suffered in the fall.

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Practice cave rescue inside Ogof Ffynnon Ddu

Peter Francis, of the South Wales Caving Club (SWCC), said the man is "fit" and his vital signs are holding up well.

Describing how he was injured, he said: "The caver was very unlucky here. He's an experienced caver, a fit caver. And it was a matter of putting his foot in the wrong place.

Image: Cave rescuers gather near the site

"He wasn't in a dangerous part of the cave, it's just something moved from under him."

The man is believed to have gone into the cave system with a group, who managed to get out and call for help.

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The severity of his injuries is unclear but he has been placed on a stretcher and rescuers are using a device that puts hot air into his lungs.

Eyewitness, by Becky Johnson, news correspondent

By a small entrance to the vast cave system beneath the Brecon Beacons a team of rescue workers are waiting with a stretcher, hoping their colleagues deep inside the cave will be able to bring the injured man out safely.

It’s an anxious wait, the rescue made harder by fog and rain.

As darkness falls there’s resignation the conditions are too poor for a helicopter to be here to carry him to hospital once he’s out.

But after more than 48 hours rescue workers are hopeful their mission is now in its final stages.

They’re giving regular updates to the family of the man who’s in his mid 40s and an experienced caver.

Now 70 of the 250 strong team of rescuers are currently underground for the final push to get him out.

The cave is treacherous, narrow passages with vertical drops - some stretches filled with water.

There will be relief once he’s out - but until then the work continues.

They have been focused on keeping him warm so he does not catch hypothermia.

Mr Francis said he hopes that the caver will be extricated today but he is not sure if that will happen.

He said getting him out could take a long time because the route is "like a maze" and needs to be rigged. It has become the longest rescue operation in South Wales' caving history.

Image: Rescuers congregate as a man has been injured and trapped in the cave system since Saturday

"The worst thing that could happen is that we dropped him in the stretcher or something like that and injured him even more," he said. "So we've got to safeguard him in advance."

The South and Mid Wales Rescue Team said in a statement: "The incident has continued during the night.

Image: There are several entrances to the cave system

Ogof Ffynnon Ddu: Britain's deepest cave

At a depth of 309.5m (1,013.8ft), Ogof Ffynnon Ddu (OFD) is the deepest cave system in Britain. It is also the third-longest, stretching for 60.6km (37.6miles) under the Brecon Beacons in South Wales.

The cave system is a Site of Special Scientific Interest (SSSI) and owned by Natural Resources Wales, which is part of the Welsh government. There are five entrances to OFD, which are all gated and only accessible with keys given out by the South Wales Caving Club (SWCC).

SWCC only give out keys to permit holders, who have to be members of caving clubs that are affiliated to the British Caving Association (BCA) or equivalent national body. Groups of cavers granted access to OFD are limited to groups of no more than six and must have "adequate experience and suitable clothing".

SWCC stresses that cavers "enter at their own risk" and "many sections of the cave are arduous". It also does not monitor the caves, so groups "must make their own arrangements for rescue".

Between 2,000 and 2,500 trips are made to OFD by cavers every year, mostly at weekends, according to SWCC. The caver currently stuck due to his injuries entered the site through the Cwm Dwr entrance and is being brought out by a team of at least 242 rescuers at the top entrance, Sky News correspondent Becky Johnson reported from the scene.

"We are moving the casualty towards the top entrance of the cave, which is located up on the mountain behind Penwyllt."

At least eight rescue teams from across the UK have joined the operation, including 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.

Image: An ambulance was among the vehicles on the scene

At midday, Sky's Becky Johnson was told there were 242 people involved in the effort.

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 over 30 miles.

Only experienced cavers are granted permission to explore inside.