AKIPRESS.COM - The operation to free 12 boys and their coach trapped in a cave in northern Thailand is running "smoothly", the head of the operation says.

Four boys have been brought above ground so far in good health, BBC reported citing rescuers.

The mission has then been paused for at least 10 hours as air tanks need to be replaced.

Rescuers decided to go ahead with the hazardous operation on Sunday because of fears of rising waters.

The next phase would begin on Monday morning, after relaying "all of the air tanks and all systems along the way", Chiang Rai Governor Narongsak Osottanakorn said.

He corrected earlier reports that said six boys had been freed.

Divers have been guiding the boys through darkness and submerged passageways towards the mouth of the Tham Luang cave system. They have reportedly been able to make the last part on foot.

Rescuers took advantage of a break in the rain to launch the mission much earlier than originally expected.

The first phase has also been conducted much faster than officials had predicted.

The group and their families had all given their agreement that they should be moved as soon as possible, said Mr Narongsak.