The boys, aged between 11 and 16, went missing with their 25-year-old coach after soccer practice on 23 June, when they had set out to explore the cave complex near the border with Myanmar.
The first boy rescued exited the cave 5:40 p.m. local time, followed by three of his team members shortly after.
"Today is the D-Day for the rescuers", said Narongsak Osottanakorn, the outgoing governor of Chiang Rai province.
The 12 Thai boys and their soccer coach will be accompanied by divers and will have to navigate tight passageways filled with muddy water as part of their rescue mission. "They have not been moved to Chiang Rai hospital yet", Tossathep said. "Finding the boys doesn't mean we've finished our mission".
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The Thai navy Seals Facebook page posted that an additional two boys had also been freed - the third at 7.35pm local time and the fourth 12 minutes later. The boys were rescued wearing full face masks.
"We're ready for the operation today", said Narongsak, who said the weather and the water levels in the cave are good.
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On Sunday four members of the "Wild Boar" team were successfully brought out from the cave, after authorities decided they had to rush ahead with a rescue operation to beat monsoon rains.
The entire operation to rescue all 13 could last two to four days, depending on weather and water conditions, said army Maj.
The potential for rising water and the dwindling oxygen levels added to the urgency of getting the team out.
The boys sounded calm and reassuring in handwritten notes to their families that were transported by divers and made public Saturday. During this process, rescuers need to hold their oxygen tanks in front of them and swim pencil-like through submerged holes.
"Don't be anxious, I miss everyone". They gave a deadline of 9:00 am to clear out, setting off a frenzy of moving and packing. "I had been anxious about my son, that he would be exhausted, he would be tired", he said.
In one, Pheerapat, nicknamed "Night", whose 16th birthday the group were celebrating in the cave when they became stuck on June 23, said: "I love you, Dad, Mum and my sister". "Night loves Dad and Mom and brother, don't worry about me". CNN's Jonathan Miller reported that the eight boys and coach who remain stranded in the cave would likely have to stay put for a couple of days due to issues restocking oxygen supplies.
Thai officials said Friday that oxygen levels inside the cave plummeted to a risky 15% - shy of the US Department of Labor's Occupational Safety and Health Administration's "optimal range" of oxygen, which is between 19.5% and 23.5%.