"We are so happy that today we could rescue another four kids", Narongsak Osatanakorn, the head of the joint command centre coordinating the operation, announced at a press briefing on Monday evening.
Narongsak said after the first four boys were rescued that they would be quarantined "for a while because we are concerned about infections".
He said the mission would resume within "10 to 20 hours".
The eight boys brought out by divers over the previous two days are in "high spirits" and have strong immune systems because they are soccer players, a senior health official said.
Torrential rain had not affected conditions for the rescue operation.
The boys underwent x-rays and blood tests and two who had signs of pneumonia were given antibiotics and are in a "normal state", he said, adding they will all remain under observation in hospital for a week.
For the first four rescues on Sunday, two divers accompanied each boy, one from the side and one from behind.
They were celebrating a second triumph after divers guided four more boys through tight passages and flooded caverns to safety Monday.
Rescuers working at a cave site in northern Thailand have suspended operations for the day after bringing four more boys out of the flooded cave system on Monday.
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More rescue efforts to free the remaining five boys and their coach are underway.
Officials lavished praise on the Thai and global divers who executed the risky rescue mission, guiding boys who can barely swim and have no diving experience through a treacherous 4-kilometre-long (2 1/2-mile) escape route that twisted and turned and rose and fell inside the mountain cave complex.
Thai soldiers arrive at the Tham Luang cave area as the operations continue for those still trapped inside the cave in Khun Nam Nang Non Forest Park in the Mae Sai district of Chiang Rai province on July 9, 2018.
They are then taken to hospital in Chiang Rai.
Monday's mission involved 18 divers from Thailand and overseas.
Two elite British divers, Rick Stanton and John Volanthen, were the first rescuers to reach the group and are believed to be part of the team. Narongsak on Monday said their identities were being protected out of respect for the families of those still trapped inside the cave. Add Thailand Cave Rescue as an interest to stay up to date on the latest Thailand Cave Rescue news, video, and analysis from ABC News.
The Thai rescue effort has been assisted by experts from around the world, and the death of a former Thai Navy SEAL diver who ran out of oxygen in the cave on Friday underscored the dangers of the mission.
Another and perhaps more worrying concern was that oxygen levels in the complex were falling close to risky levels.