A flash flood unleashed by heavy rains has trapped 27 hikers in an underground cave in western Austria, but rescue workers say they are not in danger.

The rescue officials say the hikers have been cut off from the outside world since Wednesday, when the waters flooded the entrance to the cave about 320 kilometres west of Vienna.

One of the officials, Gernot Salzmann, said the crews are in voice contact with those inside, adding that they will be taken out once the waters recede.

More In: World | International | News