Chiang Rai governor Narongsak Osotthanakorn said at a press conference on Monday that the effort would involve the same divers. Sunday's mission took nine hours and plenty of energy, with each child being accompanied by two divers along the way.
Still, the original four were undergoing medical checks in a hospital in the provincial capital and were not yet allowed close contact with relatives due to fear of infections.
The second phase of the rescue mission began around 11 a.m. local time (midnight ET) and took several hours.
Expert climbers, divers and Thai Navy Seals have mulled contingencies ranging from drilling an escape route through the mountain to waiting out the monsoon inside the cave.
Multiple calls to senior government officials and military personnel leading the operation to rescue the members of the youth soccer team rang unanswered Monday evening.
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.
On Sunday, officials decided they could no longer wait, as conditions were "as ideal as they will be". "(But) the mission is not over yet", Prayut said.
He said that the decision to try to rescue the boys and their coach was made because conditions inside the cave were the best they could hope for and that water levels were low enough after days of good weather that it was possible to walk through long stretches of the passage. Divers have taught the boys to breathe through full-face scuba gear for the areas they must swim underwater.
Each had to wear an oxygen mask to enable normal breathing, authorities said.
Four boys and their soccer coach remain in the cave. It takes the divers about eight hours to get into the cave, reach the boys, and bring them back out. In a letter of his own, coach Ekapol Chanthawong apologised to the boys' parents for the ordeal.
Thirteen global divers and five Thai Navy SEALs are involved in the operation. Days after the stranded team was found, a former diver in the Thai SEAL unit died after volunteering to enter the caves and place air tanks along the path.
When it was realised that the boys were in the cave system, divers began the process of trying to find them in the enormous area.
UPDATE 0841 ET: The rescue operation has been suspended for the night in Thailand.
But although the eight were rescued, there were concerns they may have contracted an illness while in the cave.
Narongsak Osatanakorn, the head of the joint command centre coordinating the operation said: "The factors are as good as yesterday ..."
Thai authorities say they have resumed operations to rescue members of a boys' soccer team trapped in a flooded cave after successfully getting four of the boys out on Sunday.
Shortly after, ambulances were seen racing toward the nearby city of Chiang Rai down roads that had been cleared of traffic to smooth the journey.
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