There were several concerns that prompted authorities to move forward with the plan to dive the boys out.
Unconfirmed reports that the boys' coach, Ekapol Chanthawong, 25, was among the first four to be evacuated because of the poor state of his health, were dismissed on Monday.
The third phase of the operation to begin in "20 hours".
Thai authorities said the second phase of the operation to rescue a youth soccer team trapped in a flooded cave was underway Monday, a day after four boys were pulled from the complex after more than two weeks underground.
Four more young football players were rescued Monday from a flooded cave on day two of a risky rescue mission that so far has been an outrageous success.
According to the Associated Press, a Thai official revealed that the healthiest boys were taken out of the cave first.
But he could not confirm if all five would come out today.
Thailand's Meteorological Department said there was a 60 per cent chance of rain with more thunderstorms forecast throughout the week. The operation has now been suspended after the death of a Thai military diver, and in order to restock supplies for the effort.
After his visit, he went to Chiangrai Prachanukroh Hospital to visit the rescued boys.
"All 12 wild boars and the coach have left the cave. all safe".
Rescue workers dived deep inside a flooded Thai cave for a second straight day on Monday in a treacherous bid to save a trapped group of young footballers, with the mission chief promising more "good news" after four of the 13 were saved.
Elon Musk's Space X rocket company is testing a "kid-sized submarine" that could be sent to help boys trapped in a flooded Thailand cave.
The saga has also dominated global headlines, with the team spending nine days unaccounted for inside the cave, before British divers found the emaciated and dishevelled group huddling on a muddy bank above the flooding.
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Monsoon flooding cut off their escape route and prevented rescuers from finding them for nearly 10 days.
Rescuers have been navigating a unsafe and complicated plan to get the children out under the threat of heavy rain and rising water underground. He's been watching the operations closely and says he knows some of the elite divers who have been brought in to help with the operation. "I've been involved in cave rescue for 30 years and I can not even think of one that was more complicated".
Getting to and from where the boys are has been an exhausting round trip, even for the experienced divers.
Thai military medical personnel walking inside a restricted area as preparations are made to transport rescued boys from Tham Luang cave to a hospital.
The boys' nightmare experience - trapped in claustrophobic darkness by rising waters - resonated across the globe, riveting people both in Thailand and internationally who anxiously watched the news coming from this town along the border with Myanmar.
Four boys were extracted Monday, the Royal Thai Navy confirmed.
But after the first four emerged late on Sunday afternoon, hopes began to rise of a fairytale ending to the ordeal.
Each had to wear an oxygen mask to enable normal breathing, authorities said. There was no word on the condition of the fifth boy brought out earlier on Monday.
The head of the rescue mission, Narongsak Osottanakorn, said last week they would bring the fittest people in the group out first. A nutritionist is monitoring their diet and has recommended that they eat nothing spicy or salty - despite the boys' cravings for spicy basil pork and rice, and grilled pork.
Narongsak said they will be "kept away" from physical contact with their parents until the risk of infection is over, he said, adding doctors will decide on family visits "at a distance or through glass".
Narongsak defended the lack of public disclosure of the names of the boys who had already been guided to safety, saying it "will create ill feeling" if their names are released while others languish inside the cave.
"We have not been told which child has been brought out".
"I'm hoping for good news", he said.