The source said the boys arrived at the chamber at 4pm after being rescued by foreign and Navy Seal divers from the ledge where they had sheltered from floodwaters for more than a week.
Anupong said the four boys rescued on Sunday were safe but need to undergo detailed medical checks.
Night's relatives have said they believe the group went to the cave to celebrate his 16th birthday after a Saturday football practice and got caught as heavy rains caused the water inside the cave to suddenly rise. The diver, the first fatality of the rescue effort, was working in a volunteer capacity and died on a mission to place oxygen canisters along the route., necessary for divers to safely travel the five to six hour route to where the boys are.
Health experts with the rescued boys will be checking oxygen, malnutrition, dehydration, post-traumatic stress and other psychological effects, CNN reports.
Even their mothers and fathers have been unable to visit them.
Rescuers had planned to take a 10- to 20-hour pause in the rescue efforts to replenish the cave with oxygen and give the team of 18 divers leading the boys on the hard journey a chance to rest.
Osatanakorn told reporters that four of the seven boys were brought out and taken to the hospital in the town of Chiang Rai, the provincial capital, for evaluation, and the next phase of the operation will resume after about 10-20 hours.
Earlier Monday, Narongsak said the four rescued the day before were in good spirits.
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However, after news of the rescue of four boys emerged, Musk tweeted, "Hopefully useful". Thai navy SEALs are leading the effort, but more than 90 rescue workers from around the world have been laboring in and around the dark, twisting cave.
As of Monday morning, nine people remained trapped in the cave, including the team's coach. Having completed this section, the boys are then handed over to separate, specialist rescue teams, who help assist them through the remainder of the cave, much of which they can wade through.
Musk willingness to help manifested itself since last week, when he said he will be sending a Boring company team to the site.
Police and military personnel use umbrellas to cover around a stretcher near a helicopter and an ambulance at a military airport in Chiang Rai on July 9, 2018, as rescue operations continue for those still trapped inside the cave in Khun Nam Nang Non Forest.
They are being kept separate from their families at present because of infection fears, authorities said.
The saga has 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.
"I'm hoping for good news", he said. Rescuers sought to take out the boys in the weakest condition first.
The rescue team is scrambling to extract all of those stranded before fresh rains complicate the task or cut off access by increasing flooding in the cave.