The Kathmandu-bound bus had left Khotang district in the morning. The vehicle rolled down the road at Barkhetar of Arkhanle in the district.
The wreckage was trapped between trees, making it difficult for rescuers to pull out survivors. Also, it took hours for the first rescuers to reach the site because of the mountainous area.
Bodies of 17 men and 7 women have been recovered, a police official was quoted as saying by The Himalayan Times.
The number of passengers aboard the bus was initially 28, but it swelled to 70 when some people boarded the vehicle mid way, the report said.
Nepal is mostly mountainous and most roads are narrow. Bus accidents in the country are generally blamed on poor roads and ill-maintained passenger vehicles.
Buses are usually crowded and people often travel on the roofs.