The local governor supervising the rescue mission said Saturday that mild weather and falling water levels over the past few days had created appropriate conditions for an underwater evacuation, but that they won't last if it rains again.
"I confirm that we are at war with water and time from the first day up to today", he said. "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".
On the question of dipping oxygen levels in the cave, he said rescuers had managed to establish a line to pump in fresh air and had also withdrawn non-essential workers from chamber three - where the rescue base is - to preserve levels inside the cave.
The group entered the cave on June 23 and got trapped as floodwaters tore in.
The Thai footballers, aged 11-16, have been stuck in darkness deep underground after setting off to explore the cave with their 25-year-old coach after training on June 23. Brothers from Thai SEALs are taking good care of me.
"On behalf of the global 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.
Another, Tan, wrote: "Mum and Dad don't worry about me, I'm fine".
"Please don't worry", the boys said in a collective message before each wrote short personal messages to their loved ones. Get ready to take me out for fried chicken.
Divers Friday night brought out poignant letters written by those trapped inside.
"Don't worry about me", wrote Ekkarat "Bew" Wongsookchan, 13.
Mom, Dad, Nick loves both of you and younger sibling too.
Thai navy SEAL commander Arpakorn Yookongkaew said the volunteer diver, Saman Kunan, had been placing compressed air tanks along an exit route to assist the boys in their escape from the cave.
Rescuers found them 10 days later and are now working to find a way to get them out. The narrow passages between the ledge on which they were found and the daylight outside are now filled with the cold, murky water.
The correspondence was posted on a Thai Navy SEALs Facebook page early on Saturday that said the letters were brought out on Friday night.
One of the boys appeared to be wearing a red replica England shirt like the one worn by the team during their World Cup victory over Colombia.
The massive operation inside and around Tham Luang Nang Non cave suffered its first death Friday when a former Thai navy SEAL passed out underwater and could not be revived.
The strategically placed air canisters allow divers to stay underwater for longer during what is about a five-hour trip to reach the stranded team.
Thai authorities are racing to pump out water from the flooded cave before more rain is forecast to hit the northern region.
Among his tweets about the rescue, he also said: "But let's not submit to the bad mood entirely".
Elon Musk, the entrepreneur behind the Tesla automobile and the SpaceX rocket company, has said he would send engineers to help.
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