MAE SAI, Thailand — When the owner of the youth soccer team trapped in a cave complex in northern Thailand received a call from one of the boys’ parents just after 5:30 p.m. Sunday, he knew almost instantly: The first of the Wild Boars was free.

“You could tell by his voice,” said Kamol Chanthapun, one of the founders of the Moo Pa, or Wild Boars, soccer squad that has been stranded by floodwaters since June 23. “It was the first time he sounded light.”

Four members of the team were rescued Sunday by divers who helped them navigate a treacherous path out of the cave. Ambulances raced through the streets of Mae Sai and helicopters circled overhead. The provincial governor said the four were checked out in a field hospital near the cave and then flown 37 miles south to a hospital in Chiang Rai, where an entire floor has been reserved for the rescue effort.

“Everybody is perfectly healthy,” said Narongsak Osatanakorn, the outgoing governor of Chiang Rai province. “The operation is going better than expected.”

But eight young players and their 25-year-old coach remain deep in the vast cave network, where they face depleting levels of oxygen and the prospect of rising water. Because all the equipment was used up in Sunday’s rescue attempts, the next push would have to wait until Monday morning, Narongsak said.

Heavy rains have started falling over the lush mountain range that houses the cave, adding urgency. Rescuers have been racing against the clock to get each of the boys, ages 11 to 16, none of whom knew how to swim, physically and mentally prepared for a 2.5-mile journey that will probably take at least five hours.

A Sunday evening news conference after the dramatic rescue of the four boys began with claps and cheers from some journalists. Narongsak relayed that the first of the boys was rescued at 5:40 p.m. and the second 10 minutes later. The third and fourth left the cave at 7:40 and 7:50 p.m.

According to infographics released by the Thai government, the boys were each attached to a diver, with another positioned behind them, as they made their way through the dark, murky waters that have clogged the cave’s passageways. Each boy was fitted with a face mask connected to a compressed air tank. At especially narrow parts of the cave, the tanks had to be released from their backs and rolled through.

Officials said conditions Sunday were as perfect as they could be. Water levels in the cave were the lowest they had been throughout this mission, and the first few chambers the group had to pass through — all of which were flooded days ago — were dry. Oxygen levels, too, stabilized following fears that the chamber the group was in was filling with carbon dioxide from members of the large rescue operation.

But those conditions were unlikely to hold up, as rains fell almost relentlessly throughout the day. Officials had previously said they were especially worried about rising water levels complicating the dive and negating their efforts to pump water out so the boys could walk through sections of the cave.

Narongsak said he was calling a meeting Sunday night with every person involved in the rescue effort, from doctors to those monitoring oxygen levels in the cave, to figure out a plan for those who remain. The next phase of the mission will take at least 10 hours to restart, he said, but not more than 20.

Experts have warned that even in the best of conditions, extraction efforts will bear significant risk, underscored by the death of a diver early Friday. Former Thai navy SEAL Saman Kunam was placing compressed air tanks along the exit route when he ran out of oxygen, fell unconscious and died shortly after.

The same risks remain for the team, which could exhaust the air supply before reaching safety, said Tony Haigh, a spokesman for the British Cave Rescue Council, two of whose members found the boys nine days after they disappeared.

The other risk is becoming trapped by an obstacle they cannot see because the divers’ field of view will be limited in the muddy water.

“Clearly, there is a huge risk of someone panicking if they are not used to the diving environment. It happens to adults in the open water, never mind children in a dark cave,” Haigh said. The boys have been given extensive diving lessons since being found. “I’ve no doubt some will be more apprehensive than others.”

The divers on the international team assisting the effort are from the United States, Australia, China and Europe. 

President Trump tweeted Sunday that the United States is “working very closely” with Thai officials.

Authorities for days had been stalling on a firm decision on the best way to extract the boys and their coach. Late Friday, Narongsak acknowledged that all options appeared too risky and that officials were looking for alternatives to the dive, spooked by the SEAL’s death.

Authorities said efforts to drill down from the top of the mountain have been unsuccessful, with only 18 workable openings. Impending rains made that option less viable, as it would take too long.

Before the rescue attempt was announced Sunday morning, ambulances were seen zipping up a muddy pathway to take their stations. Officials moved the large media contingent away from the rescue site to make way for those working directly on the extraction. 

As the rescue began Sunday evening, a lack of official information led to chaos and confusion, with conflicting reports of how many boys had been freed and when. Kamol and the others affiliated with the soccer team, including their head coach, said they had to stay away from social media and the news to avoid disappointment. 

“I really tried to not look at my phone,” said Nopparat Khanthavong, the team’s head coach. When the rescue of the four boys was confirmed, though, he received dozens of calls and hundreds of messages from friends, family members and those who knew the team. One message featured a cartoon rabbit with its eyes welling up in tears of relief. 

The drama of the rescue, with all its euphoric peaks and anxious lows, has gripped the world, prompting experts from all over to weigh in on possible extraction methods that would minimize risk to the boys. SpaceX chief executive Elon Musk said his team was working on a child-size submarine pod that would be “small enough to get through narrow gaps.” It was unclear whether his method would be ready in time or used by Thai officials.

Mental health and medical experts have warned that even if the whole team gets out safely, they are likely to face weeks, if not months, of recovery from mental and physical trauma. Officials had said earlier that three in the group, including the coach, were weak and malnourished. Mental health effects could include depression, anxiety, anger and an inability to adjust to normal sleep patterns, said Jacob Hyde, an assistant professor of military psychology at the University of Denver who studies reactions to isolated, confined environments.

The group’s camaraderie, however, would probably help them after the ordeal, he said.

“Cultural factors have and will continue to come into play here,” Hyde said. “If this were a group of boys who didn’t know each other and were trapped in this cave, the process and outcomes would likely be quite a bit different.”

The three-day mission to free 12 young soccer players and their coach from a flooded cave in northern Thailand has come to an end, officials said July 10. (Amber Ferguson, Melissa Macaya/The Washington Post)

The assistant coach with the boys in the cave, Ekapol Chanthawong, has been using his experience as a novice monk to help the team stay calm through meditation, officials and parents have said. Others leading the soccer team say they have recommended that all 13 go for a nine-day meditation retreat together when they are all deemed healthy.

The coach and the boys have been communicating with their parents through letters, telling their loved ones not to worry and specifying their most pressing food cravings.

“If we can get out, please can you bring me to eat at the pan-fried pork restaurant?” one of the boys wrote in a letter published on the Thai navy SEALs’ Facebook page. “I love you.”

In another post on the Facebook page, the SEALs said their group was united in bringing out the Wild Boars, posting the message with a photo of three people gripping each other’s wrists.

“Hooyah,” the post said in English.

Panaporn Wutwanich and Jittrapon Kaicome contributed to this report.