Four boys who have been trapped inside a Thai cave for 15 days have been rescued, as authorities race against time to free the remaining nine members of the group.

Confirmation of the initial rescue was posted on the Thai Navy SEAL official Facebook page late Sunday.

The first of the four boys emerged approximately nine hours after a team of 13 international cave diving experts and five Thai Navy SEALs entered the cave to begin the treacherous attempt to accompany the boys one by one through the flooded, narrow tunnels.

Families of the boys have been waiting for hours for news since authorities announced the rescue attempt would commence at 10 a.m local time Sunday, as storm clouds threatened to dump more water on the flooded caverns, undoing efforts to drain them.

"Today is D-day," Chiang Rai's Governor Narongsak Osotthanakorn declared earlier in the day.

Previously, the entire round trip through the cave network was thought to take roughly 11 hours to complete, but efforts to drain the tunnels of flood water appear to have shortened the journey time.

Twelve boys -- aged between 11 and 16 -- and their coach, were discovered by two British divers on July 2, nine days after they disappeared during an outing in the Tham Luang Nang Non-cave complex, in Chiang Rai, northern Thailand.

Those still inside the cave are perched on a small muddy ledge four kilometres (2.5 miles) inside the cave, surrounded by flood water and with a limited supply of oxygen. (CNN)