In this image made from video taken Sunday, June 24, 2018, rescue teams gather at the entrance of a deep cave where a group of boys went missing in Chang Rai, northern Thailand. Officials say multiple attempts to locate the 12 boys and their soccer coach missing in a flooded cave in northern Thailand for nearly two days have failed, but that they will keep trying. Image Credit: AP

Bangkok: Search and rescue teams in Thailand were looking on Monday for 13 members of an under-16 soccer team trapped in a flooded cave complex deep inside a mountain.

The boys' bicycles and boots were found at the mouth of the Tham Luang caves, in the northern province of Chiang Rai, after they went missing late on Saturday.

They were believed to have been trapped by rising waters inside the cave network when heavy rain hit.

Members of a navy "seal" unit including a team of divers, are searching the cave system.

"The team went down to a depth of 5 metres  and found a large chamber ... but we've found no trace of the children," the navy unit said on its Facebook page.

A navy commander overseeing the search said he was hopeful the 12 twelve boys and their 20-year-old coach would be rescued.

"I believe they're all still alive but they might be exhausted ... we should get good news today," Rear Admiral Arparkorn Yookongkaew told Reuters.

People wanting to explore the cave are meant to get permission. Thailand is in the middle of its rainy season when caves can flood.