Thai coach will be among the last group to leave the cave.

Bangkok PostThere will be four groups, with the first group consisting of four people, followed by groups two, three and four, with the coach being among the final group escorted by divers from Tham Luang cave, a military official in charge of the operation said earlier that the effort could take two to four days to complete, depending on weather conditions and water levels.

The Thai government also released a graphic showing how the rescue operation would be carried out. Two divers would accompany each boy, wearing full breathing masks and guided by ropes. In narrow passages, the divers would drop the tanks from their backs and slowly roll them, guiding the boys through. From section three of the cave system, they would walk to the entrance.

Thai authorities this morning sent 18 elite divers into Tham Luang cave, including 13 foreigners and 5 Thai SEALs, to begin the process of rescuing people one by one. The rescue operation began at 10am and as early as 9pm, the first person was released from the cave.

The boys, aged under 16, and their 25-year-old coach have been trapped in the Tham Luang cave for 15 days, after entering the cave on June 23 and becoming trapped by rising water levels. They were found by British divers on the evening of July 2 after a nine-day search involving teams from around the world.

Since July 7, water levels have dropped significantly and officials say they are at a point of "maximum readiness".The boys are in good spirits and "ready to go". Their families have been informed of the plan and are in agreement. An Australian doctor has assessed the boys' health and given the go-ahead for the journey.