Low temperatures and avalanche risk make the search very difficult, mountain rescuers said, mentioning that chances are the two tourists might not be found alive.
The tourists, a man and a woman, on Saturday contacted the mountain rescue services by cell phone to say they were trapped in Caraiman Valley on Bucegi mountain.
Rescuers were deployed to the area, but search efforts were slowed because of the dark and strong winds.
There were no reports of further contact between rescuers and the stranded tourists.
Rescue attempts will be resumed on Monday.