Chiang Rai, Thailand (CNN) A medical assessment of the 12 boys and their football coach stuck in a cave in Northern Thailand concluded that it was too dangerous to try to move the group out Thursday, according to a member of the Thai Navy SEALs who is not authorized to speak to the media.
The SEALs have started to pump oxygen into the chamber.
Separately, a new doctor's report highlighted that two of the boys and the coach were suffering with exhaustion from malnutrition.
Fresh details of the operation underway at the Tham Luang Nang Non to free the team were emerging, as rescuers pushed ahead with multiple plans to extricate the group trapped underground for almost two weeks.
More rain is forecast this weekend, putting pressure on rescuers to formulate a plan to extract the boys before flood waters rise any higher.
Huge volumes of water are being pumped out of the cave complex each day, but the narrow, winding passages inside are still flooded, meaning diving through the murky water is currently the only way in and out.
Rescuers entering the cave complex located in northern Thailand have to navigate dark, flooded tunnels for six hours to reach the team. It takes another five hours to return to the entrance.
An additional 30 SEALs arrived on site to reinforce rescue operations, according to Captain Supachai Thanasarnsakorn, deputy chief of the Thai Navy SEALs. They join the 80 already involved in the rescue operation comprising active, reserve and former SEALs.
Around the camp which has sprung up near the cave entrance, Thai military divers have set up an encampment with diving gear and equipment, while people from the local community hand out food to rescuers, other volunteers and the small army of press on site.
The boys were in good spirits despite spending almost two weeks underground, Chiang Rai governor Narongsak Osottanakorn said.
"I confirm here again that they are in good health and they are smiling and playing around," he said.
The last images the world saw of the boys was on Wednesday in a video where they introduced themselves one-by-one, saying "I am healthy."
Since they were found late Monday local time by a duo of British expert cave divers, Thai Navy SEALs have stayed with the team, tending minor wounds and giving them food to build up their strength.
The boys remain weak after spending days in the darkness, barely moving from the small, muddy ledge, away from the water.
While rescuers are trying to pump enough water out of the cave to allow the boys to simply walk out, Thai Navy SEALs are also teaching them how to scuba dive.
The boys would need to wear full-face diving masks to enter the narrow tunnels in moving water, though many experts say this would be a dangerous option for novice divers.
In an attempt to maintain the boys' morale, rescue teams have prioritized installing a line of communication between the boys and their parents.
However, they were still attempting to connect them Thursday after earlier efforts failed when the line became damaged after falling into water. CNN saw an old-style military phone and loops of cable being carried into the cave by engineers.
As divers work in tunnels deep below ground, teams are also scouring the hillside above the caves, looking for possible entry points to the chamber where the boys are sheltering.
"We are drawing our jungle trekking resources together. There are about 20 to 30 teams," Osottanakorn said.
"Now we are going to walk around that area to search every inch, (to see if) there are chimneys or holes where we can climb down, and we may adjust our plan."
The teams searching for another route through a natural chimney were dispatched following reports that the boys had told divers they heard dogs barking, a rooster crowing and children playing, possibly indicating a shaft leading up to the surface.
"There has been reports that kids have heard sounds from chickens and birds," Ben Reymenants, a Belgian who owns a diving shop in Thailand and has been assisting with the rescue efforts, told CNN.
"Were those hallucinations or did they really hear it? Because that would mean there is livestock nearby or at least a forest which would make an alternative entrance possible."
Osottanakorn said that teams on the surface were no longer drilling into the rock to create new shafts, but are focusing efforts on finding existing chimneys.
"We are no longer digging -- we will find a way that can give us access (without digging) direct to the area where the boys are," he said.
Rescue coordinators are warily eying the skies for further downpours, which could imperil the rescue mission.
"In the previous days we were fighting with time. And now we are working against water," Osottanakorn said.
"We are draining out as much as our capacity allows. But water continues to flow in, no matter how many holes have been blocked, water still continues to pour in."
Osottanakorn said rescuers were at the mercy of the rainy season, and may have to act quickly to beat fresh downpours.
"If we must evacuate (the boys) out before they are ready due to the rain ... we will do so, but it will be the very last resort to do so," he said.
CNN Weather reports that while rain can't be ruled out, there is a likelihood that the area will remain relatively dry until at least Saturday. The chance of rainfall increases from Sunday, and alongside the increased rainfall is the threat of heavier downpours.
Thai Navy divers have brought in substantial supplies -- including food and water for at least two weeks along with aluminum blankets, with support from Australian and other international divers, according to a statement from the Australian Federal Police (AFP).
The AFP's Specialist Response Group personnel are among the many divers and support staff who have been sent by a number of nations.
The Australians on the ground "remain closely engaged in efforts to support and sustain the group, as well as in planning. This includes supporting the Royal Thai Navy to transport food, water and first aid supplies into the cave system through to the group."
They are part of an international contingent that includes teams from the US military, the UK, and China.
The Thai people got moral support from one of the 33 Chilean rescued miners who were trapped for 69 days in 2010.
"To the people in Thailand, I want to send you a message from a long distance, and also a lot of strength to the authorities and all the families of these 12 children who are trapped underground," Mario Sepulveda said in a video message.
"I have no doubt that if we pray, I have no doubt that if the government in Thailand gives all it has and makes all possible human efforts, this rescue will be a success," he said.