An ambulance was seen leaving the scene immediately afterward early Monday evening.
According to the site, he confirmed rescuers would need several hours to rest and prepare their equipment.
The team became trapped on June 23 when they set out to explore the cave after soccer practice and rains flooded the tunnels, trapping them inside.
Monsoon flooding cut off their escape route and prevented rescuers from finding them for nearly 10 days.
The fellow classmates and teachers from the same school have described to the press the preparations they have made for the boys.
"He added: "They can not decide how many of them will be able to come out for the first operation".
".I can't give you an exact number but it should be more than 10 hours but not exceeding 20 hours". A rescue operation is successful.
Four boys were pulled to safety on Sunday in a daring rescue run by Thai Navy Seals who escorted each of the four to safety after they swam a hazardous kilometre underwater. The Wild Boars' assistant coach will be in group four. That's the name of the young boys' team.
The second operation started at 11 a.m. local time Monday.
"The water level has reached the lowest it has been in ten days".
Four boys of 13 trapped in a northern Thailand cave have been brought out through an underwater evacuation, a member of the rescue team said on condition of anonymity Sunday. At the hospital, the team is being checked for airborne lung infections and bacterial infections that they could have developed after being in a damp cave environment for an extended period of time.
His visit with relatives and rescue officials last week was criticised by some Thais as opportunistic as his government faced pro-democracy protests in the capital Bangkok in recent months.
A helicopter flew the four boys to the nearby city of Chiang Rai, where they were taken by ambulance to hospital.
He said the next operation will be conducted on Tuesday.
He says: "If we keep on waiting and the rains come in the next three or four days, our readiness will decrease".
"I mean, we're a big country and Thailand is a small country". But rescuers were anxious that that would not be enough: on Friday, former Thai Navy SEAL Saman Kunan died from lack of air within the cave complex.
The boys had to learn the basics of swimming and diving before they could start the 2.5 mile journey.
Authorities have been rushing to extract the boys, ages 11-16, and their coach from the cave as the annual monsoon bears down on the mountainous region in far northern Chiang Rai province. The path out is considered especially complicated because of twists and turns in narrow flooded passages. "We have to be 100 percent confident that there is no risk to the boys before we evacuate", provincial governor Narongsak Osottanakorn said.