The treacherous rescue mission operation has begun to save 12 schoolboys and their soccer coach from deep inside a Thai cave where they have been trapped for two weeks.
The acting Chiang Rai governor has told reporters "today is D-Day" with 13 foreign and five Thai divers taking part in the rescue.
He says the divers went in at 10am on Sunday (1300 AEST) and the boys will gradually come out accompanied by two divers each. He says the earliest they will come out is 9pm on Sunday (midnight AEST).
The only way to bring them out is by navigating dark and tight passageways filled with muddy water and strong currents, as well as oxygen-depleted air.
Experienced cave rescue experts consider an underwater escape a last resort, especially with people untrained in diving, as the boys are. The path out is considered especially complicated because of twists and turns in narrow flooded passages.
But the governor supervising the mission said earlier that mild weather and falling water levels over the last few days had created optimal conditions for an underwater evacuation that won't last if it rains again.
The boys, aged 11-16, and their 25-year-old became stranded when they went exploring in the cave after a practice game. Monsoon flooding cut off their escape and prevented rescuers from finding them for almost 10 days.