Thai officials say the mission to bring 12 boys and their soccer coach out of the cave where they have been trapped has begun.
Thirteen foreign and five Thai divers are taking part in the rescue effort. Each of the boys will be accompanied by two divers. The earliest they are expected to emerge from the flooded cave is 9 p.m. Sunday, local time (1400 UTC).
Officials say it could take between two to four days before all the boys are evacuated.
Rain is falling in northern Thailand where boys and their coach are trapped on a small bit of dry ground deep in the flooded cave, adding urgency to the task of saving the trapped group.
Meanwhile, the oxygen level in the cave has dropped, taxing the bodies of the captives who have had little to eat or drink while they were missing from June 23 to Monday, when they were located deep within the 10-kilometer cave system in northern Thailand.
Constant pumping has reduced the water level inside the cave, but new rain could not only re-flood the area, but also strengthen the water currents in the narrow passages though which rescuers and the boys must swim with the help of diving gear to exit the cave.
One volunteer, an expert diver, perished Thursday while laying spare air tanks along the escape route through narrow, winding flooded passages. Saman Gunan, a former Navy SEAL, ran out of air and drowned on his swim back out of the cave. His death underscores the difficulty of training boys who have not learned to swim and have no experience with diving equipment to make a six-hour trip through conditions that challenge very experienced divers.
"I confirm that we are at war with water and time from the first day up to today," Chiang Rai Acting Governor Narongsak Osatanakorn said Saturday. "Finding the boys doesn't mean we've finished our mission. It is only a small battle we've won, but the war has not ended. The war ends when we win all three battles — the battles to search, rescue and send them home."
In the five days since they were found in the cave, the boys have written notes to their families expressing optimism and encouraging them not to worry. One boy's note said: "I'm doing fine, but the air is a little cold, but don't worry. Although, don't forget to set up my birthday party."
The 25-year-old soccer coach has written as well, thanking people for support and apologizing to the parents of the boys.