Six members of Thai football team evacuated from Tham Luang cave

Experts say the survival of 12 boys and their football coach trapped in a Thai cave may ultimately hinge on mental rather than physical toughness as rescuers figure out how to free them, a process that could take weeks or even months AFP/HO

The first two emerged at about 7pm, hours ahead of schedule.

"Two kids are out. They are currently at the field hospital near the cave," said Tossathep Boonthong, chief of Chiang Rai's health department and part of the rescue team.

"We are giving them a physical examination. They have not been moved to Chiang Rai hospital yet," Tossathep told Reuters.

Shortly after, an ambulance believed to be transporting the boys was seen leaving the area. A helicopter was then seen leaving the area for the city centre, where there is a hospital.

Minutes later, a spokesman for Thailand's defence ministry said four boys have reached the rescue base camp set up inside the complex and will walk out soon.

"Four boys have reached Chamber Three and will walk out of the cave shortly," Lieutenant-General Kongcheep Tantrawanit told AFP, referring to the area where rescue workers had set up a base.

At about 7.45pm, Reuters, citing a senior member of the rescue team, reported that six have exited the cave.

The operation to extricate the 12 Thai boys and their coach, who have been trapped since Jun 23, from the bowels of the cave began at 10am on Sunday morning. The first boys were initially expected to emerge only at 9pm.

The trapped boys were divided into four groups, according to the Bangkok Post. Four boys were in the first group, with the rest split into groups of three. The coach was in the last group.

The rescue team comprised 13 foreign cave diving experts, described as some of the best cave divers in the world, and five Thai SEALs.

They were believed to have reached the first group of boys at 4pm.

It takes at least six hours to reach the chamber where the 13 have been stranded in near darkness over the past 16 days, and no fewer than five hours to come out.

Helicopters were seen waiting outside the cave complex to lift the boys to the nearest hospital, which is about 100km away.

With fresh monsoon rains due, rescuers have warned that the window of opportunity to evacuate the boys is "limited".

Millions of gallons of water have been pumped out to make the dive in Tham Luang less treacherous.

Already, one diver has lost his life after delivering oxygen supply to the trapped boys.