The 12 boys and their football coach were discovered alive on Monday.

Divers reached them nine days after they entered the caves and became trapped by rising waters caused by heavy rainfall.

More heavy rain could see water levels rise and threaten the air pocket where the group has taken refuge.

Attempts are being made to reduce the risk of this by pumping water from the underground system.

Professional divers are battling the difficult conditions to bring food and medicines to them, highlighting the complicated nature of any rescue.

There are plans to install a phone line so the boys can talk to their families.

Earlier, the Thai military said the boys would need to learn to dive - or wait months for flooding to recede before they could get out of the caves.

Food would need to be sent in for at least the next four months if the scuba-diving option was ruled out, the military added.

It is believed that most of the group cannot swim, complicating what would already be a difficult rescue.

The Thai authorities have appealed for donations of full-face scuba diving masks small enough to fit the boys in order to reduce the risk of their breathing apparatus coming loose as they travel through flooded passageways.

The group is also in a weak state after days without food.

"Helping the kids will take time," said Admiral Naris Pratoomsuwan, of the Thai navy, on Tuesday.

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 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.

Reuters