A group of boys and their football coach are set to be rescued from a flooded Thailand cave in stages.
Thai divers have warned that the group will have to swim underwater for a distance of nearly 2km to get out.
Each of the boys will be accompanied by two expert divers as they battle through strong currents before walking 200m to the cave's exit.
Rescuers are aiming to get the group out as soon as possible before waters rise further.
The group has now got food and medical treatment - after being trapped for nearly two weeks.
A new video has been released - showing the children huddled together - and apparently in good health.
Commercial diver Thorston Lechler is volunteering with the rescue mission - he says it's full of complexities.
The training we recommend is a full face mask – an AGA mask – with positive pressure,” he said.
“The problem we have right now would be [finding] the size that fits children’s heads.”
The group may be brought out at different times, depending on the health of each person, a Thai official said.
"All 13 may not come out at the same time. If the condition is right and if that person is ready 100%, he can come out," said Narongsak Osatanakorn, the Chiang Rai provincial governor.
Mr Osatanakorn said the group are still recuperating and a daily evaluation is being made of their fitness.
There will be no evacuation if there is any risk, he said.
However, some officials fear that forecasted heavy rains this weekend could force them to bring the boys out earlier.
Thai boys are treated by a Thai Navy Seal medic, 03-07-2018. Image: Royal Thai Navy/Facebook
Authorities are still exploring other options, such as scouring the mountainside for other ways into the cave and finding faster ways to pump water from it.
Offering a glimmer of hope for the families of the trapped boys, Mr Osatanakorn said that a new cave, suspected to be connected to the complex the group are situated in, has been discovered.
Two main routes of water flowing into the cave have also been identified and blocked.