Heavy rain and swiftly rising water at a rate of six inches per hour have caused setbacks for rescuers. Thai Maj. Gen. Bancha Duriyapat said they were forced to switch off power and water pumps for fear of electrical hazards.
Divers faced complicated conditions, like being forced to contort their bodies around L-shaped bends, he said.
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Relatives of the boys have stayed in tents outside the cave entrance around the clock, despite the rain, waiting for updates. A Buddhist monk led a prayer for them Thursday morning.
Authorities remain hopeful that the team found safety in dry places on higher ground within the cave to wait.
Deputy national police chief Wirachai Songmetta said police dogs were ready to aid in the effort and crews are using all tools at their disposal.
"We won't give up. That's the key here," he said.
Crews continued to search for any shafts from the surface of the mountain that could offer another way into the blocked portions of the miles-long cave below.
U.S. Indo-Pacific Command in Hawaii confirmed a team of about 30 people had been deployed to help the more than 600 local crew in the search.
"So far today, we have been working on just kind of syncing up with our Thai counterparts because really they're the true people that have been working on the ground here and we just want to ensure we are providing the best assistance to them during this process," U.S. Air Force Captain Jessica Tait said.
Anmar Mirza, coordinator of the National Cave Rescue Commission in the U.S. and editor of the book Manual of U.S. Cave Rescue Techniques, said that in a situation like this it would seem there were only two things that could be done: pump the water down and search for alternative entrances.
If there were a high-quality map, drilling would be another possibility, but that is extremely difficult for a number of reasons and could also take days to weeks, he said, adding that it was important not to take needless risks.
Mirza said the boys' youth and health are to their advantage and if the cave is not too cold, they should be able to survive four to five days with no water and a month or more with water but no food.
"The biggest concern is them getting desperate and trying to enter swift moving water," he said.