The 'choke point': How divers navigated the most dangerous part of the Thai cave rescue.

With AAP.

As of Tuesday, eight members of a Thai boys soccer team have been rescued from the depths of a cave in the country’s north. Four remain trapped along with their 25-year-old assistant coach, Ekapol Chanthawong, who lead them into the labyrinth on June 23 before heavy rain flooded the passage behind them.

Since the group was discovered on July 2, a team of Thai Navy SEALs and experienced volunteer divers has been preparing the boys for the four kilometre journey back to the entrance. The first four were guided along the treacherous route over the course of eight hours on Sunday, while the second followed in six hours on Monday.

The most challenging section of this journey is known as the ‘choke point’ – a narrow crevice barely wide enough for a person to squeeze through.

According to News Corp, it consists of upward slope followed by a sharp bend downwards. The passage here is reportedly just 38cm at its narrowest point, meaning the boys would have pass through it alone, climbing out of the water and over the peak before descending back below the surface on other side.

“The hole is really small, I have to take off my air tank to crawl through it,” a 25-year-old Thai Navy SEAL who declined to be named, told Reuters before the rescue attempt. “As I do, I feel the edges of the hole on both my back and chest.”

This “choke point” seems very tough to traverse. 15 inches wide, in the dark, uphill, and wet. The boys will need a lot of strength, and a lot of luck. ????????#ThaiCaveRescue pic.twitter.com/yICxAANbTo

— Sheel Tyle (@sheeltyle) July 8, 2018

The boys are each being guided by two divers – one in front, one behind – as they wind through pitch darkness, trudge through thick mud, clamber over slippery jagged rocks and dive through narrow passageways swirling with cold, strong currents. A journey so treacherous it claimed the life of a highly experienced former Thai navy SEAL on Friday.

“It’s dangerous to the most experienced divers to go through,” said one diver who spoke to Reuters. “It’s pretty scary.”

The cave system, in a limestone mountain range bordering Myanmar in northern Thailand, has proven to be a formidable challenge for the international rescue coalition.

Falling oxygen levels, and with many of the boys not able to swim well, present further risks should they panic as they are guided slowly through the pitch-black waters.

“It’s very dark inside even with the spotlight,” a former veteran SEAL, who had been recalled for this mission, said. “Most of the time we work with our instinct, in some position, alone in silence and in the dark.”

The first four boys in the team were rescued in a mission involving 13 foreign divers – including six Australians – and five Thai navy Seals.

They boys are in a stable condition in hospital and being treated in a ward set aside specifically for the cave rescue, a source at the hospital said.

Authorities say the rescued boys are happy and in good health.

“This morning they said they were hungry and wanted to eat khao pad grapao,” a local governor said, referring to a Thai dish of meat fried with chilli and basil and served over rice.

Authorities have said extracting the entire team from the cave could take up to four days.