The operation to free 12 boys and their coach from a cave in northern Thailand is running "smoothly", the head of the operation says.
Four boys have been brought above ground, rescuers say.
The mission has now been paused for 10 hours as oxygen levels in the cave have been depleted.
Rescuers decided to go ahead with the hazardous operation on Sunday because of fears of rising waters.
The next phase would begin on Monday morning (local time), after relaying "all of the air tanks and all systems along the way", Chiang Rai Governor Narongsak Osottanakorn said.
The rescued boys, who were escorted out by 13 foreign divers and five members of Thailand's elite navy SEAL unit, are in good health.
Eight boys and their coach are still to be rescued.
Earlier reports said six boys had been freed.
Tham Luang rescue chief Narongsak Osaththanakorn; “I confirm again that we have successfully rescued four and it has been our masterpiece work”— amanda hodge (@hodgeamanda) July 8, 2018
Divers have been guiding the boys through darkness and submerged passageways towards the mouth of the Tham Luang cave system, where they have reportedly been able to walk the last part on foot.
Rescuers took advantage of a break in the rain to launch the mission much earlier than originally expected.
The first phase has also been conducted much faster than officials had predicted.
The group and their families had all given their agreement that they should be moved as soon as possible, said Mr Narongsak earlier.
A team of 90 expert divers - 40 from Thailand and 50 from overseas - has been working in the cave system.
The BBC's Dan Johnson, who has been at the scene, said doctors went to assess the boys on Saturday and decided on a priority list, sending the weakest out first.
Getting to and from where the boys are has been an exhausting round trip even for the experienced divers.
The process includes a mixture of walking, wading, climbing and diving - all in complete darkness - along guide ropes already in place.
Wearing full-face masks, which are easier for novice divers than traditional respirators, each boy is being accompanied by two divers, who also carry their air supply.
The toughest section is about halfway out - at a section called "T-Junction", which is so tight the divers have to take off their air tanks to get through.
Beyond that a cavern - called Chamber 3 - has been turned into a forward base for the divers. There they can rest before making the last, easier walk out to the entrance. They are then taken to hospital in Chiang Rai town.