Three researchers from Poland have been trapped in a cave in the Austrian Pinzgau region since Thursday when water ingressed.
They are stuck in the Lamprechtshöhle (state of Salzburg), also called "Lamprechtsofen".
Attempts were made to contact them on Friday.
The operations management requested special divers.
According to the assessments of the Salzburg Cave Rescue Service, there was no immediate danger to life for the men, who are believed to be about 1800 meters deep in the cave.
They are well equipped and experienced.
In addition, rescue niches with blankets and emergency equipment have been created in the cave, the front part of which is accessible to tourists.
The warm weather has caused a lot of meltwater that has penetrated and collected in a depression.
So the way back is blocked, said the operations manager, according to the Austria Press Agency.
"You can think of it like a siphon." The cavers boarded on Thursday morning to explore the tectonic structure of the region and were expected back in the evening at 7 p.m.
When a colleague noticed the water, he raised the alarm.
The cave system covers 62 kilometers, the Lamprechts Cave is considered the longest passage cave in the world.
However, the passage is lengthy and technically very demanding, experts were quoted as saying.
Therefore, this way out is just as impractical as an attempt to dive out with equipment, which requires special skills.
The divers should try to make contact and bring material or food if necessary.
The water level is expected to drop in the next few days.
In the past 20 years, groups of visitors have been trapped in the tourist part of the cave three times by water ingress, which is why an early warning system has now been installed there.