A man who got lost inside a cave in Thailand where rescue workers are searching for a group of boys and their soccer coach recalled on Thursday his experience inside the "labyrinth", saying it was a miracle he got out alive.

Thai and international rescue teams are scouring the flooded Tham Luang cave complex in Chiang Rai province to try to find the 12 missing children, aged from 11 to 16, and their 25-year-old assistant soccer coach, who disappeared, apparently after going to explore the cave on Saturday.

In 2002, Intu Incharoen and four friends also set out to explore a cave that mothers have for generations forbidden their children from visiting. They soon found themselves hopelessly lost.

"I was so lost I almost couldn't make it out," said Intu, 34.

The Chiang Rai native said parts of the cave's floor were hollow and there were numerous side channels, some dropping off down into uncharted depths of darkness.

"You could fall through some hollow ground. There were lots of diversions. It was a labyrinth. It was so deep you couldn't tell where it ended," said Intu.

The 12 boys and their coach set off into the cave after soccer practice on Saturday. Their bicycles and soccer boots were found at the mouth of the cave but there has been no sign of them apart from some footprints near the cave's mouth.

The cave network stretches 10 km (6 miles) into a jungle-clad mountain and rescue workers believe floodwaters cut off the boys in a chamber. Rescue efforts have been dogged by rising waters while heavy rain has fallen incessantly.

Martin Ellis, author of 'The Caves of Thailand Volume 2' describes how the cave is prone to flooding in the wet season which usually runs from May to October.

"It can only be explored between November and June," Ellis wrote.

Intu said he and his friends were so lost it was impossible for them to retrace their steps, back the way they had come.

Hours later, they heard women calling for help from an adjoining chamber. After following the voices, the two groups joined forces and eventually found an exit route back to the entrance.

"It was a miracle," Intu said, adding that parents have long warned their children to stay away from the cave, and for good reason.

"The cave is a forbidden place. Parents always said you could go anywhere but there," he said.