A rescue operation is under way after four men became trapped in a drift mine in the Swansea Valley.
They are stuck in a ventilation shaft at the Gleision Colliery, near Cilybebyll, Pontardawe.
South Wales Police, alerted to the incident at 0921 BST, said three other men had earlier escaped from the colliery, one of whom is in hospital.
Police, who called it a difficult rescue operation, said there is a water in the mine.
Emergency services confirmed one person had been taken to Morriston Hospital in Swansea but no details have been released about his condition.
Two people managed to escape unaided from the drift mine – a mine cut into the side of a hill where the coal seam is accessed horizontally – before emergency services arrived.
Friends and relatives of the trapped miners are being kept up to date by police family liaison officers.
BBC Wales reporter Nicola Smith said about 50 rescuers were involved in the operation of whom 18 to 20 were firefighters trained for this type of incident.
Rescuers include nine rope specialists and 12 urban search and rescue specialists.
The Mines Rescue Service (MRS) in south Wales, which sent a team of five rescuers to the colliery at 09:45 BST, said there had been no explosion or fire.
A rescue team from Mansfield in Nottinghamshire has arrived at the scene and is monitoring the air coming out of the mine.
A South Wales Police spokesman said: “Seven people were initially in the mine at the time, three of them got out – with one taken to hospital.
“It is believed the other four remain inside. A rescue operation is under way. As you can imagine, it is quite a dynamic situation.”
Local councillor Arthur Threlfall, who serves on Cilybebyll Community Council, said: “I understand the injured man was taken to hospital via helicopter.
“The mine is in quite a remote spot. At the moment you cannot go anywhere near it because a large area around it has been cordoned off by the police.”
He added: “Gleision is one of those collieries that has open and shut many times, and they tend to work on the basis of when coal is found. However, it has recently been extended.
“This is the first mining disaster I have known for many years. There are not many collieries left like there used to be.
First Minister Carwyn Jones is being kept fully aware of what is happening at the mine.
Welsh Secretary Cheryl Gillan commented: “I am receiving regular updates from the Police Services and I will be praying for the safe rescue of all involved.”
Expressing his deep concern, Neath MP Peter Hain said: “This is one of a number of small mines in the area. Obviously the families will be deeply worried.”
Meanwhile, Neath AM Gwenda Thomas said the point of the contact for the area is Rhos Community Centre where those affected can talk to police and specialists.
Although most mines in south Wales are now closed, there are pockets of small-scale collieries still in operation.
Gleision Colliery, in operation since 1993, works coal under a very steep hillside above the banks of the river Tawe.