Seven Lao citizens had entered the cave in Xaisomboun province to prospect for gold but their exit was blocked, leaving them trapped for more than a week.
Video footage showed rescuers guiding a mud-smeared man wearing a headlamp from the tight cave entrance.
Reuters had not yet verified the video at the time of writing.
It took about 37 minutes to bring him through the passages to safety, the team said in a Facebook post.
Rescuers said they had stopped operations for the night as they evaluated the remaining four people they had found, and planned to resume the search for the final two.
A team of volunteers from neighbouring Thailand joined the rescue efforts on Sunday and further reinforcements were due to arrive on Friday, including from France, Indonesia, Japan, Thailand and Australia, the group posted on Facebook.
Kengkard Bongkawong, a Thai cave diver involved in the mission, said in a Facebook post on Friday that the health of the survivors was deteriorating as they awaited rescue.
"The rescue operation is extremely challenging, as it involves moving them through narrow passages stretching hundreds of metres and requiring underwater diving," he said.
Footage taken on Thursday by Norrased Palasing, another Thai volunteer, showed survivors sitting on a ledge deep in the cave and crying with relief.
Reuters was able to confirm the location from corroborating social media footage showing two divers in the video both went into the cave for the rescue.
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