Four of the boys were safely rescued on Sunday after rescuers carried out a risky operation, amid fears the waters will rise again to a unsafe level.
Divers have entered a cave in northern Thailand to retrieve the last four members of a football team and their coach on what rescuers hope will be the final day of the mission to free them.
A doctor and three Thai Navy SEAL members who have stayed with the group since they were found more than a week ago will also leave the cave.
As reported by CNN, operations to extract the team from the cave began at 10am local time.
But then oxygen started running low in the cave, and officials also anxious the little piece of real estate the boys and their coach have could be lost.
Former Chiang Rai governor and rescue mission commander Narongsak Osotthanakorn said Monday night that it would take 20 hours to prepare for the operation, but he cautioned timings could change depending on weather and water levels. "We will complete the mission for you".
Twelve boys and their coach were stranded when they went exploring the Tham Luang Nang Non cave after a practice game on June 23.
The authorites are still keeping the eight rescued boys away from their parents for fear of infection.
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The second group of 4 that were pulled out afterwards are aged between 12 and 14.
Tuesday, he tweeted from Thailand that he had been in the caves and that a mini-sub made from rocket parts and named "Wild Boar" after the boys' soccer team, was ready if needed and would be left in Thailand in case it could be of future use.
The exact health of the eight boys has not been released, but on Monday officials said the first four boys requested a meal of pad kra pao, a chicken dish with sweet basil.
The 31cm-wide custom submarine would make the boys passive participants in the rescue and could potentially shorten the journey, which took divers a total of nine hours in the second successful rescue operation on Monday.
But the early signs were promising, with X-rays and blood tests showing just two had signs of pneumonia and that they were in a "normal state" after taking antibiotics, Jedsada said. Four boys and the coach are still deep inside, and authorities have indicated they're continuing with their so-far successful effort to bring the boys out guided by experienced divers. Tracy also noted that the glimpse we've seen of the trapped boys showed they appeared to be in good spirits.
The 8 boys who have already been taken from the cave by diver are thought to be largely healthy after their ordeal, despite having been trapped inside the cave with little food or water for more than two weeks.
A witness near the cave told the Reuters news agency that medical workers carried four people to emergency rescue vehicles.
"Although his technology is good and sophisticated, it's not practical for this mission", Osatanakorn said after the press conference.