A major search and rescue operation is underway for 12 boys and their soccer coach who are missing in a flooded cave in northern Thailand.

The boys, aged 11 to 15, are believed to have entered the Tham Luang Nang Non cave with their coach late Saturday afternoon.

Anguished parents of the members of the boys’ soccer team have spent three nights without their children as water continues to rise in the sprawling caverns, suspending rescuers’ search on Monday.

However, officials remain optimistic the boys will be found safe.

“We went in a few kilometres and were able to enter a second chamber behind the entrance. In that chamber, there was an area where I saw shoes and bags left behind on the ground. We believe the students have gone further in,” SEAL team member Naponwath Homsai said.

Despite heavy rain and rising water, officials hope there are still safe spaces within the cave.

“We’re confident that the kids should still be in good condition,” Chiang Rai Deputy Governor Passakorn Bunyalak said.

During Monday’s attempt, divers were unable to reach a large chamber deep inside the cave where the students might be, according to an official at the forest park in Chiang Rai province, where the cave is located.

The passage to the chamber is extremely small, flooded and “covered with sand and mud”, forest park official Kamolchai Kotcha said.

Further attempts also failed to locate the boys, though rescue teams have found “traces” of them inside the cave, police in Mae Sai district said.

“Right now, our family is hoping that the children trapped inside will have formed a group and are safe and waiting for officials to go in and save them in time. That’s what I’m hoping,” the father of one of the missing boys, Noppadol Kantawong, said.

Footage on Thai television showed bicycles and backpacks left outside the entrance to the cave.

 -with agencies