About a dozen navy divers have re-entered a partly flooded cave in Thailand as they joined rescuers searching for 12 boys and their football coach who have been missing for three days in the sprawling caverns.

Divers have been seeking a way forward through the chambers of the Tham Luang Nang Non cave complex, but flooding has hindered their progress.

The authorities have also been seeking alternative ways in, using helicopters and search parties on foot to find holes that might exist in the ceilings of other parts of the cave.

Rain that fell overnight has added to the difficulties of exploring inside the cave.

However, the initial chambers near the cave’s entrance are dry, and a power line was extended inside to provide light and ventilation and help the divers communicate with those outside.

The boys, aged 11 to 16, and their 25-year-old coach were believed to have entered the cave in Chiang Rai province on Saturday afternoon.

A mother reported that her son did not return from football training that day, setting off the search.

Thailand cave
A bike left by one of the missing boys outside the flooded cave (Tassanee Vejpongsa/AP)

Relatives of the missing boys and others performed a ritual on Tuesday morning calling for those who are missing. They played drums and gongs and two relatives held fishing nets as symbols to fish out lost spirits from the cave.

Organiser Jiratat Kodyee said the ritual was a traditional way of showing support for the boys’ families.

Navy Lt Naponwath Homsai said the divers would enter the water after they reach a chamber further inside that was flooded almost to its ceiling on Monday.

“We hope that the water level has gone down, but we will have to see,” he said. “Today we will try to find passages under the water that hopefully will lead to other chambers.”

The cave complex extends several miles and has wide chambers and narrow passageways with rocky outcrops and changes in elevation. Still, officials have said they are hopeful the boys found a safe space away from the floods.

Rising waters on Monday evening frustrated efforts to search further in the cave, and the efforts were halted temporarily.

Parents waited overnight in tents outside the cave entrance as rain poured. Medics sat in a tent nearby, and bicycles and backpacks the boys left behind remained at the entrance.

Lt Naponwath said on Monday that other shoes and bags belonging to the group had been left in a cave chamber. “We believe the students have gone farther in,” he said.

Authorities have said footprints and handprints were found inside the cave complex, and that tourists trapped there by past floods have been rescued after the waters receded.

Officials are hopeful there are still safe spaces in the cave complex despite the flooding.

The cave, cut into a mountainside near the border with Burma, can flood severely during the rainy season, which runs from June to October.