Cave divers in Thailand are poised to restart the high-risk operation to extract the remaining eight boys and their football coach from a vast flooded cave system.
Four boys were brought safely out of the cave on Sunday.
But the mission was paused overnight for air tanks to be replaced.
The boys became trapped in the cave on 23 June after heavy rains caused flooding, but were found alive last week by divers.
Rescuers decided to go ahead with the hazardous operation to free them because of fears that waters would rise again.
Activity at the dive site early on Monday suggests that the operation may have resumed or be about to resume. But there has been no confirmation.
At least seven ambulances have driven towards the cave entrance.
The BBC’s Jonathan Head says this is a tightly controlled operation, and the identities of the boys who got out are being kept secret – it is not clear whether even their families have been told.
Rescuers took advantage of a break in the rain on Sunday to launch the mission earlier than some expected.
The first stage of the mission ran “smoothly” and the rescued boys were in “good health”, according to the Thai authorities.
But with heavy rainfall overnight and more forecast for the coming days, divers will need to work quickly to free those still trapped. On Saturday, Narongsak Osottanakorn, governor of the Chiang Rai province, said that teams had a three to four-day window to carry out their operation.
How are the boys being moved?
A team of 90 expert divers – 40 from Thailand and 50 from overseas – has been working in the cave system.
They have been guiding the boys through darkness and submerged passageways towards the mouth of the Tham Luang cave system
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 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 his air supply.
The toughest part is about halfway out at a section named “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 the boys can rest before making the last, easier walk out to the entrance. They are then taken to hospital in Chiang Rai.
In an indication of how dangerous the journey can be, a former Thai navy diver died in the caves on Friday. Saman Gunan was returning from a mission to provide the group with air tanks when he ran out of oxygen.
He lost consciousness and could not be revived. His colleagues said they would “not let the sacrifice of our friend go to waste”.
