How the rescue will take place.

The world was watching with bated breath as it was hoped an attempt to free the 12 starved boys and their 25-year-old football coach would be made on Thursday. However, the rescue operation has been postponed at least another day.

"We hope that today or tomorrow the water level between the third chamber and the point that the students are at will decrease more," a senior Thai rescue official said, according to Fairfax.

"The water level between the third chamber and the boys is still high. We put the tubes at the third chamber, trying to get the water out as much as possible."

The boys are reportedly being trained in how to breathe with scuba equipment.

The danger zone: A flooded passage linking the caves will be the rescue operation's greatest obstacle. Photo / News.com.au

But diving experts have warned that the mission is extremely dangerous as the boys can't swim and have never used scuba gear, and the cave's narrow passageways pose a significant challenge for even the best cave divers.

A narrow 3km flooded stretch of the Tham Luang Nang Non cave, which took experienced cave divers about three hours to navigate, poses an ominous hurdle for the inexperienced boys in the desperate rescue plan.

British Cave Rescue Council chairman Gary Mitchell told the BBC that freezing, muddy water was touching the roof of the cave inside the pitch black passage, which is extremely narrow — so much so that it is only big enough to fit one person through at a time.

A Thai diving website, Digitalay, has posted a sketch that shows how divers must tackle the dangerous 3km stretch.

Rescuers lay telephone cable from a cave where a young football team and their coach are trapped. Photo / AP

Volunteers holding a rope guideline would be submerged by 10m at each flooded point in the passage and divers would have to dismount their scuba kits to stand any chance of getting through.

As each boy is dragged through the dangerous passage while closely tethered to a diver navigating the tight nooks and crannies, there is a risk of their gear being knocked off.

The diving site reported that Belgian cave diver Ben Reymenants, who owns a business in Phuket, had discovered and placed a guideline in a new, wider channel with occasional air pockets, which should make the extraction easier and safer.