Thai officials had said earlier this week that the boys were practicing breathing in diving masks in case heavy rain forces the group to swim and dive out the same way rescuers entered. But on Thursday, authorities told ABC News that they are no longer pursuing that option amid concerns that something could go awry or the boys could panic underwater.
Instead, authorities said rescue crews will focus on pumping out water from flooded passageways leading to the chamber inside Tham Luang Nang where the boys and their coach were found on July 2. They are also drilling into the rock inside the cave to widen some of the narrow passageways while crews outside continue scouring the region's rugged jungle-covered terrain for any natural shafts that connect to the cave network below.
Thai officials are working with engineering experts to build a stone dam at a stream located south of Tham Luang Nang Non to divert the flow of water into the vast cave complex. Thai Public Broadcasting Service (TPBS), a public and independent broadcaster in Thailand, reported that officials expect the water level inside the cave to decrease by approximately 30 to 50 centimeters per hour within the dam. Pumping can reduce the water level by 1 to 2 centimeters per hour.
"We [were] racing against time before we found them," Chiang Rai provincial Gov. Narongsak Osatanakorn told reporters Thursday. "Now we are racing against water."
The boys, between the ages of 11 and 16, hiked into Tham Luang Nang Non, Thailand's longest cave, with their 25-year-old soccer coach after practice on June 23. It's believed that the coach often brought his team to the popular tourist site in mountainous Chiang Rai province for fun excursions.
But as the group ventured deeper into the complex, the sky opened up and it began to rain, flooding the cave and cutting off their escape. The group forged ahead before finding a raised, dry chamber where they were stranded in total darkness.
Thai officials launched a massive search and rescue operation in Khun Nam Nang Non Forest Park involving more than 1,000 people, including specialists drafted from various nations such as Australia, China, Japan, the United Kingdom and the United States. The search and rescue teams tried anything they could to locate the boys and their coach -- deploying ultrasonic sensors into the cave, drilling through the rock and dropping survival packages down holes they found above ground in hopes the supplies would reach the group.
More than a week later, two British cave divers found all 13 alive on a slope called Nern Nom Sao that's about three miles from the cave's main entrance. It took the divers, John Volanthen and Richard Stanton, nearly six hours to navigate through a treacherous maze of caverns and tunnels, both dry and flooded, with some barely wide enough for their diving equipment.
"On each journey in and out of the cave complex," the Thai government said in a statement Thursday, "the rescue team has to spend a total of 11 hours maneuvering through the narrow and slippery cave corridors."
Thai authorities said Royal Thai Navy members, a medical doctor and a nurse have been looking after the group ever since, providing them with high-protein drinks and medical assessments. While they were in relatively good shape, some of the boys complained of being weak from stress and lack of food while others suffered from minor injuries, such as scrapes and cuts.
Crews are also working on installing electricity and a fiber optic phone line in the cave so the boys can speak with their families waiting anxiously outside.
"Currently, all 13 are regaining physical strength while the water level is continuously decreasing. Thirteen sets of life-saving equipment have been prepared for them," the Thai government said in its statement Thursday.
Rescuers took advantage of the relatively dry weather this week by pumping out as much water as possible from the cave. Thai authorities said Thursday that the pumping has been "carried out efficiently," with only one chamber adjacent to Nern Nom Sao slope under water.
"The current obstacles are the imminent rainfall and the narrow and slippery trails in the cave," the Thai government said. "Rescuers and doctors are constantly assessing the weather condition and the survivors’ health in order to come up with an appropriate extraction plan."
Thai groundwater specialist Tsanet Natisri told ABC News his team is focused on pumping out groundwater as well as surveying the surrounding area to locate and divert any water sources flowing into the cave complex.
"We got to do it before the rain comes. When the rain comes, the water in the cave is going to fill up and it is going to be hard to take the kids out," Natisri told ABC News in an interview Thursday.
An official with Thailand's National Broadcasting and Telecommunications Commission told ABC News that rescuers want to wait until the water level inside the cave recedes so the boys can float out in life jackets.
Monsoon rains are forecast to pummel the region Sunday as Thailand enters its wet season. It's unclear how much more time rescuers need before attempting an extraction.
"What we worry most is the weather," the Chiang Rai provincial governor told reporters Thursday. "We can't risk having the flood back into the cave."
ABC News' Brandon Baur, Matt Gutman and Anthony Trotter contributed to this report.