Water levels are rising inside a cave in Thailand where 12 boys and their soccer coach have been missing for four days.

Large hoses and pumps are being used in the rescue effort at the Tham Luang Nang Non cave in Chiang Rai province, where Navy Seal divers say water levels are rising at a rate of 15 centimetres per hour.

Interior Minister Anupong Paojinda told reporters on Wednesday that elite divers leading the search were seriously handicapped by muddy water that has filled some chambers of the large cave to the ceilings.

He said the divers can proceed only when enough water is pumped out so there is space between the water and the ceiling to make it safer to work.

An army officer briefs relatives near the cave. Photo: AFP/Getty

The divers will also soon start using special oxygen tanks that provide longer diving times, he said.

The boys aged 11 to 16 have been missing since their 25-year-old coach took them to the cave complex on Saturday after a practice match. Officials have previously said they believe they are still alive.

Somkuan Saokeaw, a volunteer rescue worker who had just left the cave area where a diving team was operating, said they had worked through the night in the farthest chamber they could access.

A family member looks at a photo of a missing child. Photo: AFP/Getty

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

Authorities have said footprints and handprints were found inside the cave complex, as well as other items thought to belong to the boys.

-AAP