By Kocha Olarn, Chris Lau, Charlotte Reck, CNN

(CNN) — Cave divers are squeezing through narrow, flooded corridors in a delicate operation to reach seven villagers trapped underground in a cave in Laos for nearly a week.

The villagers went into the cave in the central Laotian province of Xaisomboun last Wednesday in search of gold, but heavy rain triggered flash flooding which blocked the exit, the Associated Press reported, citing Laos and Thai rescue teams.

Two Thai divers and a Finnish expert who helped in the 2018 dramatic cave rescue of a young soccer team in Thailand joined the risky operation Monday.

The villagers are believed to be trapped deep inside the cave on “an elevated ledge inside the cave that benefits from continuous airflow,” state-run Lao News Agency reported.

But the expert divers conducting the rescue mission expressed hope that all who are trapped will be found alive.

“We think they should survive,” Thai diver Kengkad Bongkawong told CNN on Tuesday, explaining that the location of the men inside the cave is the “safest spot.”

To reach them, rescuers will have to navigate a 340-meter (1,115 feet) tunnel, according to the Metta Tham Kalasin (MTK)Command and Control Center, one of the groups coordinating the rescue.

Some parts of the tunnel are just 60 centimeters (23 inches) wide, so rescuers will need to crawl to get closer to the trapped group, the command center posted to Facebook. Images showed cables laid through a gap between the rocks to guide rescuers to its lower reaches.

Bongkawong described the natural entry point to the cave as a path that plunges downward at a 45-degree angle.

“It is so narrow that you have to tilt sideways, duck low, and crawl flat on your stomach to get through,” the seasoned diver explained.

He added that entering and exiting the cave must be carefully coordinated as there is no space for rescuers to cross one another.

Helmets, breathing masks and gas monitors are being used to monitor the level of oxygen and toxic gases in the narrow cave system. An ‘airline’ is also being used to pump in fresh air from outside the cave.

Video filmed inside the cave, posted on the Facebook page of a Thai rescuer, showed rescuers moving in dark caverns almost filled with water. Efforts are being made to pump water out of the tunnels to make them easier to access.

Outside the cave, a rope team was dispatched on rappelling mission to scan for possible routes to reach the villagers from four shafts that were spotted on the mountain above the cave, the group said.

The rescue operation is unfolding in a mountainous area near Long Tieng in Xaisomboun province, known for its sweeping valleys and rich mineral reserves.

Rescuers are using a map of the cave that Bongkawong said is highly accurate, aiding the team’s efforts.

“That’s why I believe, given the geography and the living conditions of the victims, if they are in that specific area, their chances of survival are very high – very high,” he said.

Authorities were alerted to the trapped villagers by a member of the group who managed to escape before the exit was blocked, AP reported, citing Bounkham Luanglath, who leads Laos’ Rescue Volunteer for People.

Bongkawong explained that the man who escaped had done so by wading through the water and effectively forcing his way out, something only a local familiar with the area would know to do.

“We call it ‘boo’ out,” Bongkawong said, revealing that there is a specific term in the local dialect for the action the man took.

Villagers frequently visit the site to search for gold deposits despite repeated safety warnings from the authorities, Luanglath said.

CNN has reached out to Laos’ Ministry of Foreign Affairs for comment. The Southeast Asian country is a one-party communist state that closely monitors the release of information.

In 2018, 12 boys and their soccer coach became trapped deep inside a cave in the northern Thai province of Chiang Rai for more than two weeks when a downpour flooded the tunnels.

A massive rescue operation featuring experienced divers from Australia, the United Kingdom and the United States saw the boys removed one by one through the cave network in a heroic mission that captivated audiences around the world.

Bongkawong also participated in the remarkable rescue effort, and told CNN how the two operations compare: “Tham Luang was difficult to search; this cave is difficult to access.”