Rescue workers are fighting to save two cavers in Poland after a narrow tunnel flooded with water, blocking their exit on Saturday.
More than two dozen rescuers are attempting to reach the pair inside the Wielka Sniezna cave, the longest and deepest in the Tatra mountains.
Contact is yet to be established with the cavers and concern is growing.
Preparations are being made to use explosives to blow open a route into the cave.
"The only way to get to them is through a series of very complicated pyrotechnic actions," Jan Krzysztof, head of the Tatra Volunteer Search and Rescue group, told TVN.
"We have the necessary materials, but this will take a long time," he added.
"We have to be ready for work that could last days if not weeks."
The two became trapped inside the cave on Saturday and the alarm was raised by others on the excursion.
Flooding is complicating the rescue effort.