In Thailand the search of a cave complex for 12 boys and their soccer coach is now into its eighth day.

Navy divers, who have joined the rescue operation, are navigating their way through 3km of dark, flooded cave passages to reach the spot where rescuers believe the missing group would have the best chance of survival.

There has been no contact with the boys, aged 11 to 16, or their 25-year-old coach since they went off after soccer practice to explore the vast Tham Luang cave complex in Thailand's northern province of Chiang Rai.

With the way out blocked by flood waters caused by heavy rains, rescuers are hoping that they made it through to an elevated rock mound in one of the underground chambers far under the mountain.

Cavers have nicknamed the potential safety spot "Pattaya Beach" after one of Thailand's best known tourist destinations.

Rear Admiral Apakorn Yuukongkaew, commander of Thailand's elite Navy SEAL unit said divers had reached 'chamber three', having been driven back by rising flood waters when they reached the same point earlier in the week.

"From chamber three to the intersection and then onto Pattaya Beach, this area is all flooded and dark," Mr Apakorn told reporters.

"It's about 3km from chamber 3 to Pattaya Beach."

The race to save the boys has dominated news bulletins, gripping the nation, and relatives of the missing children have kept up a long vigil at the mouth of the cave.

Dr Somsak Akkasilp, director-general of the Medical Services Department, said the group's survival depended on whether they found fresh drinking water, but he was concerned about the risk of infection from unclean water, or contact with some animal inside the cave.

"They should be okay without food for eight days," he said.

Rescue teams have also been scouring thick jungle on the mountainside for alternative routes into the cave.

Helicopters were seen flying over the cave complex this morning dropping supplies to police and other rescue teams that camped there overnight.

Yesterday, members of a police search team were lowered down a 50-metre shaft drilled from the surface to the cave, but it was unclear what progress they had made.