They ventured in while the cave was dry but were caught out by a sudden deluge of rain, which flooded the system. It is still unclear how the boys will be rescued from the range of unsafe options on the table, as the country holds its breath hoping for good news. The path out is considered especially complicated because of twists and turns in narrow flooded passages.
Urgency Builds| Pressure is mounting on Thai authorities to bring forward a rescue plan for 12 boys and their coach trapped deep inside a flooded cave in northern Thailand, after the death of a former navy diver and a drop in oxygen levels underground, CNN reports. But the prospect of fresh monsoon rains and more flooding threatens to unpick the progress.
"Once his mission was over he dove back, but in the middle of their return his buddy found Samarn unconscious in the water and tried to pump his heart, but he could not save his life", the SEAL unit said in a statement. But, he added, "we will have to continue our mission as planned".
One, identified as Tun, wrote: "Mom and Dad, please don't worry, I am fine". I've told Yod to get ready to take me out for fried chicken.
Another boy, 13-year-old Sompong "Pong" Jaiwong, put on a courageous face: "Dear Mum and Dad, I love you. I promise to take the very best care of the kids", he said in a note given to a diver on Friday.
Ekkarat Wongsukchan (Bew): Don't worry about me, dad and mum.
Peerapat "Night" Sompiangjai, 16: "I love Dad, Mum and brother".
One boy named Mick wrote: "Don't be anxious, I miss everyone". "Don't worry and don't forget my birthday".
Teacher, don't give us lots of homework!
The elite diver's death underscores the difficulty and complexity of attempting to rescue the 12 boys, ages 11-16, and their 25-year-old coach. Don't worry about Tern, I can take care of myself.
"On behalf of the worldwide football community, I would like to join you in expressing my deepest sympathies and support to the families of the players and coach, as well as my solidarity with the people of Thailand at this time of great concern", he wrote.
While the oxygen level had stabilised he warned levels of "carbon dioxide are another factor" in considering when to move the group - in addition to impending rains which could cover much of the muddy ledge on which the group are sheltering.
Divers took the boys letters written by family members camped outside the cave but an attempt to send down a phone failed earlier this week.
Rescuers have been unable to extend a hose pumping oxygen all the way to where the boys are, but have brought them some oxygen tanks.
Relatives of the missing boys show photos of them after the 12 boys and their soccer coach have been found alive in the cave where they've been missing for over a week after monsoon rains blocked the main entrance on July 02, 2018 in Chiang Rai, Thailand.
Narongsak said they would have to drill through 600 metres (1,970 feet) of fragile limestone rock to reach the boys and were discussing drilling angles. The 13 are having health evaluations and rehabilitation, and being taught diving skills.
But the difficulty of getting them out was emphasised on Friday when Saman Kunan, a 38-year-old former Thai Navy Seal died after laying oxygen tanks along a potential exit route.
He further discussed ideas over Twitter with James Yenbamroong, CEO of Thai space startup mu Space Corp. on the possible ways that he could work in the rescue mission.
It's taken even experienced rescue divers up to five hours to safely navigate the unsafe cave channels to reach the team.