Medics appeared to remove one person on a stretcher but hid the person's identity behind multiple white umbrellas.
After the ambulance was seen leaving the complex at around 5 p.m. Monday, a helicopter took off. But authorities have said it remains unclear how long the boys would have to remain inside.
Narongsak Osottanakorn, the Chiang Rai governor and head of the rescue mission, said that "today, everything was smooth".More news: Conte takes Chelsea training amid doubts over future
Eight boys and the coach remain trapped, and experts are hoping to free the rest of the boys today.
The rescue operation to save a Thai soccer team from the flooded Tham Luang Nang Non caves in northern Thailand began in earnest on Sunday, with an experienced team of divers rescuing four of the 13 members.
Worldwide rescue teams from the U.S., China, Australia and Europe are stationed along tunnel walls from the entrance of the cave to chamber 3, a safe command center inside the cave, to support the extraction.
Complicated rescue: Local government officials said 13 foreign and five Thai divers are taking part in the long and unsafe operation to free the 12 young soccer players and their 25-year-old coach.
Earlier in the day, divers began the 2.4-mile journal of attempting to remove the 12 boys and soccer coach from the cave. However, it only took 7 hours and 40 minutes. As per reports, the boys have been trapped in the cave since June 23. Their condition was not immediately clear.
Authorities in northern Chiang Rai province began the risky mission to bring out the 12 boys and their football coach earlier on Sunday.More news: Thai Cave Rescue Operation Suspended After 4 More Boys Freed
Elon Musk is testing equipment created to help rescue the remaining members of a Thai youth soccer team who are trapped in a cave, the Tesla CEO tweeted on Sunday.
The operation, which started on Sunday morning, will take two to three days to complete, as each round trip from the rescue camp in the cave to the site where the boys and their coach are located takes 11 hours.
Authorities temporarily stopped their efforts Monday to replenish air tanks along the cave's treacherous exit route.
To get the boys out, divers will be forced by the narrow passages to accompany them one at a time.
"We've been working continuously overnight", a Chiang Rai government source told AFP on Monday morning, requesting anonymity, and confirming that there had only been a pause of the actual extraction operations.
"It's highly risky, it's very precarious and our thoughts are not only with the boys but also with the diving and rescue teams that are assisting", Bishop told the Nine network on Monday.
Bursts of heavy monsoon rain soaked the Tham Luang cave area yesterday and storms were expected in the coming weeks, increasing the risks in what has been called a "war with water and time" to save the team.More news: Judge cites 'real progress' in reuniting migrant families
The rescue has captured the world's attention, and many have offered their ideas on how to get the team out.