The avalanche hit 4 a.m. Sunday when most of the climbers were sleeping at a base camp nearly 23,000 feet in elevation. Many of the victims are from France, Germany and Spain.
Poor weather conditions have made searching for any possible survivors difficult. The rainy monsoon season has just ended in the Himalayas, making conditions unpredictable.
The cause of the avalanche was not immediately determined.
Avalanches don't happen often on Mount Manaslu. The last deadly avalanche to take place there was in 1972, when an avalanche buried a team of climbers and killed six Korean and 10 Nepalese guides.
Nepal is home to eight of the world's 14 highest peaks. Mount Manaslu is 26,760 feet high and is considered one of the easier peaks to climb.
The Associated Press contributed to this report.