The bus flipped over and fell about 20 feet onto a river bed, NTV television footage showed. Deputy Gov. Mehmet Seyman of the Mediterranean province of Antalya said rescue workers struggled to pull the bodies and injured from the wreckage.
NTV television, citing local authorities, said the driver was sleeping at the wheel.
Each year, thousands of people are killed in traffic accidents on Turkey's roads because of careless driving or poor road conditions. Many of the roads consist of just two lanes, are badly lit and poorly patrolled by police.
The bus was traveling from the resort of Alanya, which is popular with Russian and German tourists, to the scenic Pamukkale waterfall near the central city of Denizli.
About 3 million Russian tourists visit Turkey annually. Earlier this month, Turkey and Russia agreed to mutually lift entry visa requirements for visits of up to 30 days in an effort to boost tourism and business.