Rescuers in northern Thailand on Sunday extracted four members of a youth soccer team from the cave where they had been trapped for more than two weeks, part of an ongoing operation to rescue the 12 boys and their coach.

The head of the operation said it was going “better than expected.” The operation to rescue the boys, ages 11-16, and their 25-year-old coach by having them dive out of the flooded cave began this morning, with expert divers entering the sprawling complex for the complicated and dangerous mission.

Chiang Rai acting Gov. Narongsak Osatanakorn, who is heading the operation, said the four boys had been taken to a hospital.

“The operation went much better than expected,” Narongsak said at a news conference, adding that the healthiest were taken out first. He said the next phase of the operation would start in 10-20 hours.

The entire operation to rescue all 13 could last two to four days, depending on weather and water conditions, said army Maj. Gen. Chalongchai Chaiyakam.

Just after 9 p.m., Thai navy SEALs posted on their Facebook page again, saying: “Have sweet dreams everyone. Good night. Hooyah.” Narongsak said earlier in the day that 13 foreign and five Thai divers were taking part in the rescue and that two divers would accompany each boy as they’re gradually extracted.

The only way to bring the boys and their coach out of the cave is by navigating dark and tight passageways filled with muddy water and strong currents, as well as oxygen-depleted air. A former Thai navy SEAL passed out and died making the dive Friday.

Experienced cave rescue experts consider an underwater escape a last resort, especially with people untrained in diving, as the boys are. The path out is considered especially complicated because of twists and turns in narrow flooded passages.

But Narongsak said earlier that mild weather and falling water levels over the last few days had created optimal conditions for an underwater evacuation that won’t last if it rains again.

Before announcing that the rescue was underway, authorities ordered the throngs of media that have gathered at the cave from around the world to leave.

The boys and their coach became stranded when they went exploring in the cave after a practice game June 23. Monsoon flooding cut off their escape and prevented rescuers from finding them for almost 10 days.

The ordeal has riveted Thailand and made global headlines, and the search and rescue operation has involved international experts and rescuers.

“I confirm that we are at war with water and time from the first day up to today,” he said Saturday. “Finding the boys doesn’t mean we’ve finished our mission. It is only a small battle we’ve won, but the war has not ended. The war ends when we win all three battles the battles to search, rescue and send them home.”

The boys sounded calm and reassuring in handwritten notes to their families that were made public Saturday. The notes were sent out with divers who made an 11-hour, back-and-forth journey to act as postmen.