The boys, members of a football team between the ages of 11 and 16, have been trapped with their coach in Tham Luang cave in northern Chiang Rai Province since late June.
Monsoon flooding cut off their escape and prevented rescuers finding them for nearly 10 days. Some officials said his collapse was due to his oxygen supply running out but the cause of his collapse was not confirmed.
Around 1,000 people are involved in the complex rescue operation. In the harrowing footage, rescuers progressed slowly in single file through low-ceilinged and flooded passageways where water in some places reached above their shoulders, gripping a lifeline attached to the cave wall overhead.
The Thai governor in charge of rescuing 12 boys and their soccer coach from a cave says the cooperating weather and falling water levels over the last few days have created conditions for extraction that won't continue if it rains again. They have now been trapped inside the cave for 14 days. But with heavy monsoon rains expected on Sunday, waiting may no longer be an option, Rear Admiral Apakorn Yookongkaew, Thailand's Navy Seal commander, told the BBC.
"I talk to them every day, if they'd like us to take the kids out, it has to be in the minimum risk", he said.
"We will come back tomorrow", Nasan said. It is only a small battle we've won, but the war has not ended. "Everyone is a professional so we're trying to put it away and avoid it happening again", he said, adding: "Everybody is focusing on getting these boys out - keeping them alive or getting them out".
Family and friends expressed relief when the boys were found, but video of the gaunt, disheveled lost youngsters released this week has only partially reassured their loved ones.
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Another boy, 13-year-old Sompong "Pong" Jaiwong, put on a fearless face: "Dear Mum and Dad, I love you".
One boy named Mick wrote: "Don't be anxious, I miss everyone".
"I can guarantee that three to four days from now is the most favourable time for the operation and rescue mission using one of the action plans".
One player writes: "I'm doing fine, but the air is a little cold but don't worry".
Duangpetch "Dom" Promthep, 13, called on his parents not to forget to throw him a birthday party. A diver who spent time with the boys said earlier the youngsters wanted to know the results of the matches.
"To all the parents, all the kids are still fine".
"Coach Ek acted responsibly in his capacity as an adult and a coach to take care of the children's lives and well-being", said one user. "Thank you for all the moral support and I apologize to the parents", said the handwritten note delivered to the outside world by divers.
The rescue mission began after rainshowers soaked the Tham Luang Cave area in northern Chiang Rai province for the past 24 hours, heightening the risks in what the governor has called a "war with water and time" to save the team. The 13 are having health evaluations and rehabilitation, and are being taught diving skills.