Twelve boys and their football coach trapped in a Thai cave have been found alive but will need learn to dive or wait months for flooding to recede before they can get out, the army says.

The group had been missing for nine days before they were found by divers late on Monday on a small dry ledge.

Rescuers are now battling rising water to bring more supplies to the group.

They may need to have food sent in for at least the next four months, according to the military.

How were they found?

Two British rescuer divers who had flown over to join the search operation found the boys on Monday night.

The video of that first contact was posted on Facebook by Thai Navy SEAL special forces.

The boys are seen by torchlight sitting on a ledge above water, responding to the divers that all 13 were there and that they were very hungry.

They ask how long they have been underground and whether they can leave now. The divers tell them they have to wait, but say people will come back for them.

One boy replies: "Oh. See you tomorrow."

The search for the group had gripped the nation as it was unclear where they were or whether they even were still alive.

Families of the missing group were ecstatic at news of the rescue.

How can they get out?

The Tham Luang cave complex in Chiang Rai in northern Thailand is regularly flooded during the rainy season which lasts until September or October.

If the children are to be brought out before then, they will have to learn basic diving skills.

But experts have cautioned that taking inexperienced divers through the dangerous corridors of muddy, zero-visibility waters would be a very dangerous operation.

Attempts to pump the water levels lower have so far not been successful.

If they are to wait until the water recedes by itself, it would mean the boys will have to stay in the cave for months and have to be continuously supplied with food and assistance.

Doctors will go in to carry out medical checks in the coming days to establish their condition and treat possible injuries.

Who are they?

The 12 boys are all members of a local football team, the youngest of them only aged 11.

The 25-year old coach who got trapped with them is known to have taken them on occasional excursions and field trips.

Tinnakorn Boonpiem, whose 12-year-old son Mongkol is among the 13, told AFP news agency near the caves she was "so glad" to hear they were safe.

"I want to him to be physically and mentally fit," she said.

"I'm so happy I can't put it into words," another relative of one of one of the group told reporters as tears of joy streamed down his cheeks.