The second rescue mission to retrieve the eight remaining boys and their soccer coach trapped inside a Thai cave must overcome a number of challenges if it is to be successful. Their condition was not immediately clear.
He said the rescue operation was pausing for about 10 to 20 hours to check the escape route again for safety before being resumed.
Four boys out of 12 trapped in a flooded cave in Thailand with their soccer coach have been freed as part of an ongoing rescue mission that started Sunday after the group was initially found July 2-about a week after the search for them began.
Twelve youths aged from 11 to 16 were trapped, while a massive worldwide rescue effort has been mounted including Thai Navy divers and foreign volunteers. The ambulances drove to a nearby helipad and a helicopter was seen taking off.
He added that the boys had all been assessed by a doctor and were "very fit physically and mentally". Gen. Chalongchai Chaiyakam said.
Shortly before 2am NZT, the Thai navy SEALs reported on their official Facebook page that four had been rescued. The path out is considered especially complicated because of twists and turns in narrow flooded passages.
"Now and in the next three or four days, the conditions are flawless (for evacuation) in terms of the water, the weather and the boys' health", Narongsak told reporters.
The extraction of the boys occurred more than two hours earlier than the most optimistic deadline set by rescue authorities earlier on Sunday morning.
The dozen boys between the ages of 11 and 16 are accompanied by their 25-year-old coach. The team and coach were exploring the cave after a practice game when heavy rainfall and flooding cut off their escape route out of the cave and prevented rescuers from finding them for nearly 10 days.
The rescue has received worldwide support. Very courageous and talented people!
Teams entered the cave at 10:00 local time (03:00 GMT), operation chief Narongsak Osottanakorn told reporters.
She said members of the 353rd U.S. Special Operations Group and U.S. military pararescue teams, survival specialists, divers and medical personnel are on the ground in support of the Thai-led worldwide rescue effort. "We have tried all possible ways to get the boys out, but sometimes we can't win over nature".
"We have a fraction of a second to help them come out", the governor said. The notes were sent out with divers who made an 11-hour, back-and-forth journey to act as postmen. The other boys have not been identified yet. I've told Yod to get ready to take me out for fried chicken.
"Don't be anxious, I miss everyone". Do take good care of yourself. "Love you all", wrote Mick.
"I hope that in some way our words of support may help bring them a little peace and courage in these hard moments of uncertainty and concern". Another, of indistinct origin, asked their teacher not to give them a lot of homework.
The boys and the coach will dive out of the cave one at a time, each accompanied by a member of a team of worldwide and Thai divers.
"Thank you for all the moral support and I apologise to the parents". The 13 were having health evaluations and rehabilitation, and were being taught diving skills.
The boys - cold, malnourished and exhausted - will have to swim large sections of the underground maze and squeeze through tiny gaps, some no bigger than 30cm.
ABC News reports a team of four elite divers who will lead the rescue operation, and they might be brought out in stages.
Bursts of heavy monsoon rain soaked the Tham Luang Cave area in northern Chiang Rai province on Sunday and storms were expected in the coming weeks, increasing the risks in what has been called a "war with water and time" to save the team.