Rescuers are making every effort to extract at least the strongest of the trapped footballers from a Thai cave before heavy rains forecast for Saturday, according to a military source.
A navy source, speaking on condition of anonymity, told the ABC three factors are driving the urgency — the water level inside the cave, the amount of oxygen available, and the health of the boys and their coach.
"The pressure we are experiencing comes from working against the weather, as the forecasts tell us there will be heavy rain in this area within 48 hours," he said.
The soccer team was trapped in a cave system known as Tham Luang on June 23, surviving for nine days before rescue divers found them on a muddy ledge.
The navy source said two of the boys are in a weaker condition, as is the 25-year-old coach, who sacrificed his share of their meagre food supplies to give to the boys.
The decision whether to attempt a risky dive and scramble through four kilometres of tunnels continued to dominate announcements from officials on Thursday.
The navy source said rescue coordinators face tough choices and there are differences of opinion among those providing assessments.
Boys hear sounds of dogs amid search for alternative ways out
A group of volunteers from southern Thailand who scale cliffs to get birds nests, which are prized as an exotic soup in parts of Asia, have been recalled to the rescue effort in the hope of an finding an alternative route down where the group is trapped.
It comes amid reports that the boys have apparently heard the sounds of chickens and dogs.
This has come out via two very well-known volunteers in Thailand, who are quoting the Thai Navy SEALs as getting that information from the boys.
It is not clear when they heard those noises or what it means, but the suggestion is that there may be an alternative way to get out, or at least an alternative way that the sound is coming in.
However, parents have been told that their boys may suffer hallucinations after so long underground.
Australian Defence Force and Australian Federal Police personnel are among those providing advice, but have been tight-lipped about whether to attempt an extraction or wait — possibly until the end of the rainy season around October.
Chiang Rai Provincial Governor Narongsak Osottanakorn has been the public face of the rescue effort and on Thursday gave the most detailed description yet of preparations.
"This morning, I have asked for 13 sets of equipment to be prepared and to check the equipment lists and place them inside in case we have to bring them out in this condition with less than 100 per cent readiness," said Mr Narongsak at a media briefing.
"I have asked the doctor and the SEAL team who are working on the rescue operation to assess the situation and see what risk level we can take."
"For example, if we can accept the 90 per cent safety level, and if all conditions are at that 90 per cent, then we are ready to bring them out. And that's what we are prepared for."
Diving the boys still appears to be the preferred option, according to officials, who have confirmed members of the team have started to learn to scuba dive.
The navy source said the biggest challenge for the boys would be a 200-metre stretch of completely flooded cave that makes up part of the 600-metre section between so-called "Pattaya Beach" and Chamber Three, where an operation centre has been set up.
From Chamber Three it is still another 2 kilometres to the cave entrance.
Some parts of the journey will be walkable.
The navy source dismissed reports the water level inside the cave had dropped by 40 per cent.
"Forty per cent of what?" he asked.
The source said water levels are being monitored at three key spots — the cave entrance, Chamber Three and "Pattaya Beach".