Rescue teams continue the search for the group of youth soccer players and their coach.
The boys, aged between 11 and 16, and their 25-year-old assistant coach, went missing on Saturday after soccer practice.
Conditions in the cave also proved tough for the 200 rescuers dispatched into the tunnels to find the boys.
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"Coach Aek is very dedicated to the team", said Noppadon Kanthawong, whose 13-year-old son plays on the Wild Boars but made a decision to skip Saturday's cave trip. "They'll just need to rotate". "We have a challenge from the water level that keep rising", Thai army chief Gen. Chalermchai Sittisart told reporters at the site.
Parents waited overnight in tents outside the cave entrance as rain continued to pour.
Relatives of the missing boys and others performed a ritual Tuesday morning calling for those who are missing.
While distraught relatives and friends gathered at the mouth of the cave, rescue workers pumped out water, but persistent heavy rain has slowed their progress.
"My son, come on out!"
A steady stream of visitors come to kneel down, light candles and incense and pray in front of a statue of a young woman wearing a pink traditional outfit, surrounded by flowers and other offerings.
The cave complex extends several kilometres and has wide chambers and narrow passageways with rocky outcrops and changes in elevation.
Chote Narin, an officer at Mae Sai district police station, said on Monday afternoon that footprints and handprints were found inside the cave complex.
Rescue workers took turns pumping water from inside the cave amid hard weather conditions, including heavy rain overnight which caused water levels to rise inside the Tham Luang cave in the country's northern Chiang Rai province.
The group was reported missing Saturday.
Anxious relatives gathered at the cave entrance, many having camped overnight hoping for news.
'We believe the students have gone farther in, ' he said.
Noppadon, the father of one of the team members who didn't go on the cave trip, said he brought his son to the cave Tuesday because he couldn't concentrate at school. "I still have hope".
In the myths of the northern region, there is a link between danger and caves and the idea that these risky female spirits, or Jao Mae, can also help humans who can appeal to them, he said.
Getting farther into the cave has required lots of oxygen and special diving skills, which would also complicate rescue efforts once the boys are found, officials said. Divers must navigate through darkness and kicked-up silt that can reduce visibility nearly to nothing even with underwater lights, and progress is painstakingly slow.
The cave, which is part of a national park near the border with Myanmar, is a popular tourist attraction but it appears as though the single entrance to it has now been blocked by water.