"All four boys have arrived at hospital, all are safe", Narongsak Osottanakorn, head of the rescue mission, told reporters of those rescued on Monday.
The rescue mission had called today "D-Day" because the water was at its lowest since the boys were discovered and heavy rains were forecast for later this week, giving them only four days to get all the boys out.
The Thai navy SEAL unit, which has been overseeing the rescue, confirmed on its Facebook page that the total number of boys brought out was eight. Narongsak said some are well enough to ask for solid food.
The boys had to navigate through flooded passages that are no more than two feet wide in some areas.
Should the rains further flood the cave, as predicted, the team could be trapped in the cave for more than four months until waters recede.
To get the boys out, divers will be forced by the narrow passages to accompany them one at a time.
He said the next phase of the operation will resume in between 10 and 20 hours - probably late Monday morning or afternoon - as rescuers have to replaced empty compressed air tanks and perform other maintenance on the rescue system.
However, a statement issued by the rescue operation earlier said that they couldn't confirm how many children would be brought out in this first stage of the rescue, "due to the complex nature of the cave and difficulty of the operation".
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The four boys were among 12 members of the Wild Boars team, ages 11-16, who ventured deep into the cave along with their 25-year-old coach on June 23.
It is expected that the operation will continue in the next 12 hours.
He said 13 foreign divers and five Thai navy SEALs were taking part in the key leg of the rescue: taking the boys from where they have been sheltering and through dark, tight and twisting passageways filled with muddy water and strong currents. It was unclear who was inside the ambulance or the helicopter.
But the mission was paused overnight for air tanks to be replaced.
The boys separately emerged from Tham Luang Nang Non cave in Chiang Rai Province between 5:30 pm and 6 pm local time.
Monsoon flooding cut off their escape route and prevented rescuers from finding them for nearly 10 days. After an initial assessment at the site, the plan was to airlift the boys to a makeshift helipad close to the Chiang Rai Prachanukroh hospital, some 70 km away.
"It pretty much rains all day, sometimes every day or maybe every other day, it just depends on the area where you are at", said Guerrero.
A multi-pronged rescue effort has been underway since they were found almost a week ago.
They were guided by expert divers who plotted the hours-long escape through more than four kilometres (2.5 miles) of twisting passageways and flooded chambers.