The group, including a family of three and two tourist guides, were reported to be sheltered in a safe place in the 8.2km-long Krizna Jama cave, which can only be visited by boat.

Yesterday evening, rescuers managed to reach the group briefly and delivered food, water, and a heated tent, civil protection officials from the area told journalists today.

But since the group was located more than 2km away from the entrance to the cave, it would take a new team of divers three to four hours to get to them, officials said, adding that the final rescue would depend on when the water levels fall, STA news agency reported.

That may happen overnight, but could also take a couple of days.

Krizna Jama, a chain of underground lakes with emerald green water, is the fourth largest known cave ecosystem in the world in terms of biodiversity.