Navy Seal divers and other rescuers have re-entered a partly flooded cave in northern Thailand to search for 12 boys and their football coach who have been missing for three days in the large caverns.

Divers have been trying to move through the chambers of the Tham Luang Nang Non cave complex, but flooding has hindered their progress. Officials have also been trying to find other ways in, using helicopters and search parties on foot to find holes that might exist in the ceilings of the cave.

Overnight rain added to the difficulties of exploring the cave. However, the chambers near the entrance were dry, and a power line was extended inside to provide light and ventilation and help the divers communicate with people outside. The power would also allow water to be pumped from the cave.

The boys, aged 11-16, and their coach, 25, were believed to have entered the cave in Chiang Rai province late on Saturday afternoon. The search began after a mother reported that her son did not return from football practice that day.

Relatives of the missing boys and others performed a ritual on Tuesday morning 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. The organiser, Jiratat Kodyee, said the ritual was a way of showing support for the boys’ families.

Relatives hold fishing nets as a symbol to fish out lost spirits inside the cave. Photograph: Tassanee Vejpongsa/AP

Navy Lt Naponwath Homsai said the divers hoped to reach a chamber that was previously flooded. “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. Officials have said they hope the group found a safe space away from the floods.

Parents and medics waited overnight in tents outside the cave entrance, where the boys’ bicycles, backpacks and football boots remained.

At a prayer session on Monday evening, some of the relatives walked inside the cave entrance. One woman called: “My son, come on out! I am waiting for you here!”

Namhom Boonpiam, whose 13-year-old son Mongkol is missing, said she had been waiting at the entrance since Saturday night. “I haven’t slept and I hope that all of them can come out, all safe and sound,” she said. “My son is a strong boy. I still have hope.”

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

Chiang Rai’s deputy governor, Passakorn Bunyalak, said getting rescuers further into the cave had required lots of oxygen and specialist diving skills, which would complicate recovery efforts once the boys were found. Divers might have to first take in food and the boys might need to wait out the flood or learn basic scuba skills to get out.

The cave, in a mountainside near the border with Myanmar, can flood severely during the rainy season, from June to October.